sys/ximage/ximagesink.c: Fixed a tricky race.

sys/ximage/ximagesink.c: Fixed a tricky race.

Original commit message from CVS:
2005-11-27  Julien MOUTTE  <julien@moutte.net>

* sys/ximage/ximagesink.c: (gst_ximage_buffer_free),
(gst_ximagesink_ximage_new), (gst_ximagesink_ximage_put),
(gst_ximagesink_bufferpool_clear),
(gst_ximagesink_buffer_alloc),
(gst_ximagesink_expose): Fixed a tricky race.
* sys/ximage/ximagesink.h:
* sys/xvimage/xvimagesink.c: (gst_xvimagesink_xvimage_put),
(gst_xvimagesink_expose): Fixed a tricky race.
* sys/xvimage/xvimagesink.h: