gst/base/: Implement clock sync in base class.

gst/base/: Implement clock sync in base class.

Original commit message from CVS:
* gst/base/gstbasesink.c: (gst_base_sink_do_sync):
* gst/base/gstbasesrc.c: (gst_base_src_wait),
(gst_base_src_do_sync), (gst_base_src_get_range):
Implement clock sync in base class.