An instance of GtkAdjustment may be used by another instance after
the spin button widget is destroyed. In that case, the function
gtk_spin_button_accessible_value_changed() will be called with an
invalid argument. This situation is often caused when one use
GtkCellRendererSpin widget. To avoid invalid call of the function,
the signal handler for the "value-changed" signal should be disconnected
when the spin-button widget is destroyed.
Using g_signal_connect_object achieves just that.
https://bugzilla.gnome.org/show_bug.cgi?id=691592
This commit exposes the get_type() functions and standard
headers for accessible implementations. This makes it possible
to derive from the GTK accessible implementations without
GType magic tricks. This is necessary, because we require the
a11y type hierarchy to be parallel to the widget type hierarchy.
So, if you derive a widget and need to adjust its a11y implementation,
you have to be able to derive its accessible implementation.
This commit probably exposes more than is absolutely necessary,
it also exposes accessibles of widgets that are unlikely candidates
for deriving from.
