Reworked the GstThread implementation, make more operations threadsafe and more reliable.

Reworked the GstThread implementation, make more operations threadsafe and more reliable.

Original commit message from CVS:
* gst/gstthread.c: (gst_thread_dispose), (gst_thread_sync),
(gst_thread_change_state), (gst_thread_child_state_change),
(gst_thread_main_loop):
* gst/gstthread.h:
* testsuite/threads/Makefile.am:
* testsuite/threads/queue.c:
* testsuite/threads/thread.c: (construct_pipeline), (change_state),
(main):
* testsuite/threads/threadc.c: (construct_pipeline):
* testsuite/threads/threadd.c: (main):
* testsuite/threads/threade.c: (main):
* testsuite/threads/threadf.c:
Reworked the GstThread implementation, make more operations
threadsafe and more reliable.
Moved testcases from the failing to the working list.