* glib/Object.cs: add support for native instantiation of
managed types.
* glib/ParamSpec.cs: add Flags ctor overload.
* sample/NativeInstantiationTest.cs: new sample to test the
unmanaged instantiation capability.
Based on a patch from Sebastian Dröge [Fixes#499900]
svn path=/trunk/gtk-sharp/; revision=141819
