gst/gstcaps.c: add sanity checks

gst/gstcaps.c: add sanity checks

Original commit message from CVS:
2003-12-27  Benjamin Otte  <in7y118@public.uni-hamburg.de>

* gst/gstcaps.c: (gst_caps_append):
add sanity checks
* gst/gstcaps.h: (gst_caps_debug):
remove, it doesn't exist anymore.
* gst/gstelement.c: (gst_element_threadsafe_properties_pre_run),
(gst_element_threadsafe_properties_post_run):
make debugging messages not clutter up THREAD debug category
(gst_element_negotiate_pads), (gst_element_clear_pad_caps),
(gst_element_change_state):
update to new caps API
* gst/gstinterface.c: (gst_implements_interface_cast):
don't put vital code in g_return_if_fail
* gst/gstpad.c: (gst_pad_link_try), (gst_pad_try_set_caps),
(gst_pad_link_filtered):
add pst_pad_try_link and use it.
(gst_pad_perform_negotiate), (gst_pad_renegotiate):
implement correctly, deprecate first one.
(gst_pad_link_unnegotiate), (gst_pad_unnegotiate):
add and implement.
(gst_pad_try_relink_filtered), (gst_pad_relink_filtered):
implement.
(gst_pad_get_negotiated_caps):
add and implement. Make GST_PAD_CAPS call this function.
(gst_pad_get_caps):
remove unneeded check..
(gst_pad_recover_caps_error):
disable, always return FALSE.
(gst_real_pad_dispose):
don't free caps and appfilter anymore, they're unused.
* gst/gstpad.h:
Reflect changes mentioned above.
* gst/gstsystemclock.c: (gst_system_clock_wait):
Make 'clock is way behind' a debugging message.
* gst/gstthread.c: (gst_thread_change_state):
Fix debugging message