* gtk/Gtk.metadata: virtual_method rules for GInterface generation.
* generator/ReturnValue.cs (ToNative): new method for the virtual
method generation.
* generator/Parameters.cs (FromNative): null guarding.
* generator/ManagedCallString.cs: rework for interface method
generation including callback and error param support.
* generator/CallbackGen.cs: Invoker support. new class that deals
with persistence of native and wrapper delegates in native to managed
callback method signatures.
* generator/VirtualMethod.cs: support for generation of interface
methods, and all the funky parameters that come with that.
* generator/InterfaceGen.cs: Fill out the adapter implementation.
* generator/MethodBody.cs: Initialize overload. Extend ThrowsException
to support GError outside the last parameter slot.
* glib/GInterfaceAttribute.cs: New attribute to mark interfaces and
obtain adapter type.
* glib/Object.cs (AddInterfaces): interface registration method.
* glib/GInterfaceAdapter.cs: New abstract class for interface
adapter generation.
* glib/Makefile.am: add new files.
svn path=/trunk/gtk-sharp/; revision=85658
