Revert from "edit-preferences" to "gtk-preferences"

There is not a icon named "edit-preferences" in the spec
http://standards.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html

gtk/Makefile.am

@@ -1041,7 +1041,7 @@ STOCK_ICONS = \
 	stock-icons/16/document-open.png 		\
 	stock-icons/16/gtk-page-setup.png 		\
 	stock-icons/16/edit-paste.png 			\
-	stock-icons/16/edit-preferences.png 		\
+	stock-icons/16/gtk-preferences.png 		\
 	stock-icons/16/document-print.png 		\
 	stock-icons/16/printer-error.png 		\
 	stock-icons/16/printer-paused.png 		\
@@ -1151,7 +1151,7 @@ STOCK_ICONS = \
 	stock-icons/24/gtk-orientation-portrait.png	\
 	stock-icons/24/gtk-page-setup.png 		\
 	stock-icons/24/edit-paste.png 			\
-	stock-icons/24/edit-preferences.png 		\
+	stock-icons/24/gtk-preferences.png 		\
 	stock-icons/24/document-print.png 		\
 	stock-icons/24/printer-error.png 		\
 	stock-icons/24/printer-paused.png 		\

gtk/gtkiconfactory.c

@@ -453,7 +453,7 @@ get_default_icons (GtkIconFactory *factory)
   register_stock_icon (factory, GTK_STOCK_ORIENTATION_REVERSE_LANDSCAPE, GTK_STOCK_ORIENTATION_REVERSE_LANDSCAPE);
   register_stock_icon (factory, GTK_STOCK_PAGE_SETUP, GTK_STOCK_PAGE_SETUP);
   register_stock_icon (factory, GTK_STOCK_PASTE, "edit-paste");
-  register_stock_icon (factory, GTK_STOCK_PREFERENCES, "edit-preferences");
+  register_stock_icon (factory, GTK_STOCK_PREFERENCES, GTK_STOCK_PREFERENCES);
   register_stock_icon (factory, GTK_STOCK_PRINT, "document-print");
   register_stock_icon (factory, GTK_STOCK_PRINT_ERROR, "printer-error");
   register_stock_icon (factory, GTK_STOCK_PRINT_PAUSED, "printer-paused");