check/generic/states.c: Make sure all tasks are stopped.

check/generic/states.c: Make sure all tasks are stopped.

Original commit message from CVS:
* check/generic/states.c: (GST_START_TEST):
Make sure all tasks are stopped.

* check/gst/gstbin.c: (GST_START_TEST):
Unref after usage for proper valgrinding.

* gst/gstpad.c: (gst_pad_finalize), (gst_pad_stop_task):
Really wait for the task to stop before destroying the
mutex.

* gst/gstqueue.c: (gst_queue_sink_activate_push),
(gst_queue_src_activate_push):
Small cleanups. Don't stop the task when we did not start
it.

* gst/gsttask.c: (gst_task_get_type), (gst_task_init),
(gst_task_func), (gst_task_cleanup_all), (gst_task_set_lock),
(gst_task_get_state), (gst_task_start), (gst_task_pause),
(gst_task_join):
* gst/gsttask.h:
Protect the stream lock with the object lock.
Disallow setting the stream lock when running.
Add cleanup_all to wait for the threadpool to finish.
Remove code to autoallocate a mutex if none was provided.
Add _join() to wait for a task to stop.
Protect the thread pool with a global lock.