gst/gstclock.c: Make period ids add the interval to the origial requested time instea...

gst/gstclock.c: Make period ids add the interval to the origial requested time instead of the possibly updated time w...

Original commit message from CVS:
Patch by: René Stadler <mail at renestadler dot de>
* gst/gstclock.c: (gst_clock_id_wait):
Make period ids add the interval to the origial requested time instead
of the possibly updated time which can be wrong when there are multiple
waiters for the same id. Fixes #382592.
* gst/gstsystemclock.c: (gst_system_clock_async_thread),
(gst_system_clock_id_wait_jitter_unlocked),
(gst_system_clock_id_wait_jitter):
Fix restart in the async notify thread when an async entry is added to
the front of the list. Fixes #381492.
* tests/check/gst/gstsystemclock.c: (store_callback),
(notify_callback), (GST_START_TEST), (gst_systemclock_suite):
Added test for multiple async waits.
Added test for async wait order.