gst/gstghostpad.c: More cleanups.

gst/gstghostpad.c: More cleanups.

Original commit message from CVS:
* gst/gstghostpad.c: (gst_proxy_pad_do_event),
(gst_proxy_pad_do_bufferalloc), (gst_proxy_pad_do_chain),
(gst_proxy_pad_do_getrange), (gst_proxy_pad_do_checkgetrange),
(gst_proxy_pad_set_target_unlocked), (gst_ghost_pad_parent_set),
(gst_ghost_pad_parent_unset),
(gst_ghost_pad_internal_do_activate_push),
(gst_ghost_pad_internal_do_activate_pull),
(gst_ghost_pad_do_activate_push), (gst_ghost_pad_do_activate_pull),
(gst_ghost_pad_do_link), (gst_ghost_pad_do_unlink),
(gst_ghost_pad_init), (gst_ghost_pad_dispose),
(gst_ghost_pad_new_full), (gst_ghost_pad_new_no_target),
(gst_ghost_pad_new), (gst_ghost_pad_new_from_template),
(gst_ghost_pad_new_no_target_from_template),
(gst_ghost_pad_get_target), (gst_ghost_pad_set_target):
More cleanups.
Avoid needless typechecking in macros.
Since the internal pad is always present and never changes, there is
no need to locking or ref when retrieving it.
Improve debugging a bit.
Handle link errors when setting the target. Fixes #341029.