examples/: Sync with the X server before giving an XID to our sink with a different display connection. This avoids s...

Original commit message from CVS:
* examples/play.py:
* examples/remuxer.py:
* examples/switch.py:
* examples/synchronizer.py:
Sync with the X server before giving an XID to our sink with a different
display connection. This avoids spurious X servers where the sink's
display connection doesn't know the XID that the GDK thread's does.