* atk/Atk.metadata: markup all the Ref* methods to indicate owned refs.
* generator/ReturnValue.cs: Add owned object ToNative handling.
* generator/VirtualMethod.cs: Split ToNative call from managed method
invocation to avoid duplicate calls in null checking scenarios.
* glib/Object.cs: add OwnedHandle property for use by language binding
code which needs to pass owned refs to native methods.
svn path=/trunk/gtk-sharp/; revision=99849
