Minimum GTK+2.14 required for the build.

Remove now unneeded check for 2.14 existence.

Revise direct access for '->vbox' to use gtk_dialog_get_content_area() instead.
Revise direct access for '->window' to use gtk_widget_get_window() instead.
Remove direct access for '->colorsel' and replace with gtk_color_selection_dialog_get_color_selection()
Improved usage of GTK+2.14 features for URIs.

Use gtk_show_uri() rather than own specific functions.
Use GTK+2.18 functions if available.
gtk_marshal_VOID__POINTER_UINT depreciated, use g_cclosure_marshal_VOID__UINT_POINTER instead.

Reorder parameters to match.
Rework combo boxes to work with GTK+2.24 or earlier.

Create own redirection definitions to keep the real code simpler.
If using GTK+2.24 or later don't use depreciated about dialog features as not needed any more.
[QA] Remove old checks for minimum GTK+2.10, since we require 2.14.
Don't use deprecated Gtk Type Objects - use G Type Objects instead.
Create own marshal_VOID__POINTER_POINTER function.

At some point gtk_marshal_VOID__POINTER_POINTER() is removed (in GTK3 I think).
Thus create our own version, similar to one already in print-preview.c
Merge branch 'GTK+-Updates'