Removal of all glib < 2.8 cruft since GStreamer core now requires glib >= 2.8

Removal of all glib < 2.8 cruft since GStreamer core now requires glib >= 2.8

Original commit message from CVS:
Removal of all glib < 2.8 cruft since GStreamer core now requires
glib >= 2.8
* codegen/argtypes.py:
remove gstobject cruft from ObjectArg
* configure.ac:
Require glib >= 2.8.0
* gst/Makefile.am:
* gst/pygstobject.c:
* gst/pygstobject.h:
Remove pygstobject.[ch]
* gst/common.h:
Don't include removed header file.
* gst/gst.override:
* gst/gstbin.override:
* gst/gstbus.override:
* gst/gstelement.override:
* gst/gstelementfactory.override:
* gst/gstmessage.override:
* gst/gstobject.override:
* gst/gstpad.override:
* gst/interfaces.override:
* gst/pygstiterator.c: (pygst_iterator_iter_next):
Switch from using pygstobject* functions to using pygobject* functions.
* gst/gstmodule.c: (sink_gstobject), (init_gst):
Move GstObject sink function here and use standard gobject refcounting.