gst/arg-types.py: GstMiniObject used as virtual methods parameters should be unreffed before calling the method and t...

Original commit message from CVS:
* gst/arg-types.py:
GstMiniObject used as virtual methods parameters should be unreffed
before calling the method and the ref-ed.
Added Params and Returns for const-gchar*, GType and gulong so the
code generator can generate more virtual methods handlers/proxys.
* gst/gst-types.defs:
* gst/gst.defs:
* gst/interfaces.defs:
Added vtable and virtual method definition for interfaces so we can properly use virtual
methods from those interfaces in python.