docs: correct various spelling and grammar errors

I noticed a few cases of "wether", and while fixing them noticed a few
"its" which should be "it's". It all went downhill from there.

gtk/gactionobserver.c

@@ -118,7 +118,7 @@ g_action_observer_action_enabled_changed (GActionObserver   *observer,
  * @state: the new state of the action
  *
  * This function is called when an action that the observer is
- * registered to receive events for changes its state.
+ * registered to receive events for changes to its state.
  *
  * This function should only be called by objects with which the
  * observer has explicitly registered itself to receive events.

gtk/gtkaccelmap.c

@@ -955,7 +955,7 @@ _gtk_accel_map_remove_group (const gchar   *accel_path,
  *
  * Note that locking of individual accelerator paths is independent from 
  * locking the #GtkAccelGroup containing them. For runtime accelerator
- * changes to be possible both the accelerator path and its #GtkAccelGroup
+ * changes to be possible, both the accelerator path and its #GtkAccelGroup
  * have to be unlocked. 
  *
  * Since: 2.4

gtk/gtkcellarea.c

@@ -2075,8 +2075,8 @@ gtk_cell_area_get_request_mode (GtkCellArea *area)
  *
  * Retrieves a cell area's initial minimum and natural width.
  *
- * @area will store some geometrical information in @context along the way,
- * when requesting sizes over an arbitrary number of rows, its not important
+ * @area will store some geometrical information in @context along the way;
+ * when requesting sizes over an arbitrary number of rows, it's not important
  * to check the @minimum_width and @natural_width of this call but rather to
  * consult gtk_cell_area_context_get_preferred_width() after a series of
  * requests.
@@ -2151,8 +2151,8 @@ gtk_cell_area_get_preferred_height_for_width (GtkCellArea        *area,
  *
  * Retrieves a cell area's initial minimum and natural height.
  *
- * @area will store some geometrical information in @context along the way,
- * when requesting sizes over an arbitrary number of rows, its not important
+ * @area will store some geometrical information in @context along the way;
+ * when requesting sizes over an arbitrary number of rows, it's not important
  * to check the @minimum_height and @natural_height of this call but rather to
  * consult gtk_cell_area_context_get_preferred_height() after a series of
  * requests.

gtk/gtkcellareacontext.c

@@ -30,7 +30,7 @@
  * #GtkTreeModel rows that are requested and rendered in the same context.
  *
  * #GtkCellLayout widgets can create any number of contexts in which to
- * request and render groups of data rows. However its important that the
+ * request and render groups of data rows. However, it's important that the
  * same context which was used to request sizes for a given #GtkTreeModel
  * row also be used for the same row when calling other #GtkCellArea APIs
  * such as gtk_cell_area_render() and gtk_cell_area_event().
@@ -329,12 +329,12 @@ gtk_cell_area_context_real_allocate (GtkCellAreaContext *context,
  *
  * Fetches the #GtkCellArea this @context was created by.
  *
- * This is generally unneeded by layouting widgets; however
+ * This is generally unneeded by layouting widgets; however,
  * it is important for the context implementation itself to
  * fetch information about the area it is being used for.
  *
  * For instance at #GtkCellAreaContextClass.allocate() time
- * its important to know details about any cell spacing
+ * it's important to know details about any cell spacing
  * that the #GtkCellArea is configured with in order to
  * compute a proper allocation.
  *

gtk/gtkcellrenderer.c

@@ -46,7 +46,7 @@
  * is rendered in the correct location using gtk_cell_renderer_render().
  *
  * There are a number of rules that must be followed when writing a new
- * #GtkCellRenderer.  First and foremost, its important that a certain set
+ * #GtkCellRenderer.  First and foremost, it's important that a certain set
  * of properties will always yield a cell renderer of the same size,
  * barring a #GtkStyle change.  The #GtkCellRenderer also has a number of
  * generic properties that are expected to be honored by all children.

gtk/gtkcellview.c

@@ -596,7 +596,7 @@ gtk_cell_view_size_allocate (GtkWidget     *widget,
   /* The first cell view in context is responsible for allocating the context at allocate time 
    * (or the cellview has its own context and is not grouped with any other cell views) 
    *
-   * If the cellview is in "fit model" mode, we assume its not in context and needs to
+   * If the cellview is in "fit model" mode, we assume it's not in context and needs to
    * allocate every time.
    */
   if (priv->fit_model)
@@ -993,7 +993,7 @@ gtk_cell_view_new_with_context (GtkCellArea        *area,
  * @text: the text to display in the cell view
  *
  * Creates a new #GtkCellView widget, adds a #GtkCellRendererText 
- * to it, and makes its show @text.
+ * to it, and makes it show @text.
  *
  * Return value: A newly created #GtkCellView widget.
  *
@@ -1058,8 +1058,8 @@ gtk_cell_view_new_with_markup (const gchar *markup)
  * gtk_cell_view_new_with_pixbuf:
  * @pixbuf: the image to display in the cell view
  *
- * Creates a new #GtkCellView widget, adds a #GtkCellRendererPixbuf 
- * to it, and makes its show @pixbuf. 
+ * Creates a new #GtkCellView widget, adds a #GtkCellRendererPixbuf
+ * to it, and makes it show @pixbuf.
  *
  * Return value: A newly created #GtkCellView widget.
  *

gtk/gtkicontheme.c

@@ -109,7 +109,7 @@
  * or stock items, rather than directly, but looking up icons
  * directly is also simple. The #GtkIconTheme object acts
  * as a database of all the icons in the current theme. You
- * can create new #GtkIconTheme objects, but its much more
+ * can create new #GtkIconTheme objects, but it's much more
  * efficient to use the standard icon theme for the #GdkScreen
  * so that the icon information is shared with other people
  * looking up icons. In the case where the default screen is

gtk/gtkspinbutton.c

@@ -2407,7 +2407,7 @@ gtk_spin_button_set_value (GtkSpinButton *spin_button,
  * @policy: a #GtkSpinButtonUpdatePolicy value
  *
  * Sets the update behavior of a spin button.
- * This determines wether the spin button is always updated
+ * This determines whether the spin button is always updated
  * or only when a valid value is set.
  */
 void

gtk/gtktestutils.c

@@ -130,7 +130,7 @@ test_find_widget_input_windows (GtkWidget *widget,
  * particular because the mouse pointer is warped to the key press
  * location, see gdk_test_simulate_key() for details.
  *
- * Returns: wether all actions neccessary for the key event simulation were carried out successfully.
+ * Returns: whether all actions neccessary for the key event simulation were carried out successfully.
  *
  * Since: 2.14
  **/
@@ -166,7 +166,7 @@ gtk_test_widget_send_key (GtkWidget      *widget,
  * particular because the mouse pointer is warped to the button click
  * location, see gdk_test_simulate_button() for details.
  *
- * Returns: wether all actions neccessary for the button click simulation were carried out successfully.
+ * Returns: whether all actions neccessary for the button click simulation were carried out successfully.
  *
  * Since: 2.14
  **/
@@ -197,7 +197,7 @@ gtk_test_widget_click (GtkWidget      *widget,
  * spin button arrow areas, usually leading to an increase or decrease of
  * spin button's value.
  *
- * Returns: wether all actions neccessary for the button click simulation were carried out successfully.
+ * Returns: whether all actions neccessary for the button click simulation were carried out successfully.
  *
  * Since: 2.14
  **/

gtk/gtktoolitem.c

@@ -1409,7 +1409,7 @@ gtk_tool_item_toolbar_reconfigured (GtkToolItem *tool_item)
   /* The slightely inaccurate name "gtk_tool_item_toolbar_reconfigured" was
    * choosen over "gtk_tool_item_tool_shell_reconfigured", since the function
    * emits the "toolbar-reconfigured" signal, not "tool-shell-reconfigured".
-   * Its not possible to rename the signal, and emitting another name than
+   * It's not possible to rename the signal, and emitting another name than
    * indicated by the function name would be quite confusing. That's the
    * price of providing stable APIs.
    */

gtk/gtkwidget.c

@@ -7503,13 +7503,13 @@ gtk_widget_set_receives_default (GtkWidget *widget,
  * gtk_widget_get_receives_default:
  * @widget: a #GtkWidget
  *
- * Determines whether @widget is alyways treated as default widget
- * withing its toplevel when it has the focus, even if another widget
+ * Determines whether @widget is always treated as the default widget
+ * within its toplevel when it has the focus, even if another widget
  * is the default.
  *
  * See gtk_widget_set_receives_default().
  *
- * Return value: %TRUE if @widget acts as default widget when focussed,
+ * Return value: %TRUE if @widget acts as the default widget when focussed,
  *               %FALSE otherwise
  *
  * Since: 2.18

gtk/gtkwindow.c

@@ -6576,7 +6576,7 @@ gtk_window_compute_configure_request_size (GtkWindow   *window,
 				 info->resize_height > 0 ? height : NULL);
     }
 
-  /* Don't ever request zero width or height, its not supported by
+  /* Don't ever request zero width or height, it's not supported by
      gdk. The size allocation code will round it to 1 anyway but if
      we do it then the value returned from this function will is
      not comparable to the size allocation read from the GtkWindow. */