(Object(GType)): Mark this ctor Obsolete
* gtk/Gtk.metadata: disable the generated GType ctor on Gtk.Widget
* gtk/Widget.custom (Widget, CreateNativeObject,
Widget_ParentSet): Connect to our own ParentSet event from
CreateNativeObject and the GType ctor, and keep a static Hashtable
of parented widgets, so that adding a managed widget to a
container keeps both the GObject and the managed object alive.
* generator/ObjectGen.cs (GenCtors): handle the disable_gtype_ctor
flag. Also, mark GType ctors [Obsolete]
svn path=/trunk/gtk-sharp/; revision=35885
