Make the ghostpad a parent of the internal pad again for better backward compatibilit...

Make the ghostpad a parent of the internal pad again for better backward compatibility. Don't write code that relies ...

Original commit message from CVS:
* docs/design/part-gstghostpad.txt:
* gst/gstghostpad.c: (gst_ghost_pad_dispose),
(gst_ghost_pad_new_full):
Make the ghostpad a parent of the internal pad again for better backward
compatibility. Don't write code that relies on this however.
* gst/gstpad.c: (gst_pad_activate_pull), (gst_pad_activate_push),
(gst_pad_link_check_hierarchy):
Require that parents should be GstElements in the hierarchy check.