gst/gst.c: _gst_trace_on is already provided by gsttrace.h, no need to declare it...

gst/gst.c: _gst_trace_on is already provided by gsttrace.h, no need to declare it ourselves.

Original commit message from CVS:
* gst/gst.c:
_gst_trace_on is already provided by gsttrace.h, no need to declare
it ourselves.
* docs/libs/gstreamer-libs-sections.txt:
Add 'buffers', 'check_cond' and 'check_mutex' from libgstcheck
and remove strange tcase_add_test which is outputting a warning.
* libs/gst/check/gstcheck.c:
* libs/gst/check/gstcheck.h:
Properly declare 'buffers', 'check_cond', 'check_mutex' extern
and define them in gstcheck.c instead of having every .c file whcih
includes gstcheck.h be defining its own copy and relying on symbol
interposing to marry them all, which doesn't work on Solaris.
* tests/check/elements/identity.c: (GST_START_TEST):
Don't define 'buffers' locally, it comes from libgstcheck.
* tests/check/generic/sinks.c: (send_buffer):
Fix type of variable (GstFlowReturn, not GstStateChangeReturn)
* tests/check/gst/gststructure.c: (GST_START_TEST):
* tests/check/gst/gstsystemclock.c: (GST_START_TEST):
* tests/check/gst/gstutils.c: (GST_START_TEST):
* tests/check/gst/gstvalue.c: (GST_START_TEST):
Add a bunch of casts to make various constants fit the types
they're being assigned to.