gst/base/gstbasesink.*: Repost EOS message while going to PLAYING if still EOS.

gst/base/gstbasesink.*: Repost EOS message while going to PLAYING if still EOS.

Original commit message from CVS:
* gst/base/gstbasesink.c: (gst_base_sink_preroll_queue_flush),
(gst_base_sink_handle_object), (gst_base_sink_event),
(gst_base_sink_wait), (gst_base_sink_handle_event),
(gst_base_sink_change_state):
* gst/base/gstbasesink.h:
Repost EOS message while going to PLAYING if still EOS.
Make sure that when receiving a FLUSH_START we don't attempt
to sync on the clock anymore.