an exact match for a C GObject class (i.e. BluecurveStyle),
walk up the gobject type hierarchy until we find a type
that we do have a wrapper for, and return that. This means
that you'll always, worst-case, end up with a GObject.
* glib/Value.cs, glue/value.c: Added default constructor
to GLib.Value() that creates a new value with a type of
INVALID, and changed the glue function to not call
gtk_type_init if INVALID is passed.
svn path=/trunk/gtk-sharp/; revision=7994