gst/base/gstbasesink.c: Make sync property settable from subclass.

gst/base/gstbasesink.c: Make sync property settable from subclass.

Original commit message from CVS:
* gst/base/gstbasesink.c: (gst_base_sink_class_init),
(gst_base_sink_init):
Make sync property settable from subclass.

* gst/elements/gstfakesink.c: (gst_fake_sink_init),
(gst_fake_sink_change_state):
Set sync to FALSE by default.