gst/videofilter/gstvideobalance.c: Fix regression; changing a property affects the...

gst/videofilter/gstvideobalance.c: Fix regression; changing a property affects the video stream.

Original commit message from CVS:
* gst/videofilter/gstvideobalance.c: Fix regression; changing a
property affects the video stream.
* sys/xvimage/xvimagesink.c:
* sys/xvimage/xvimagesink.h:
Add synchronous property for debugging.  Should probably be
disabled in non-CVS builds.  Make sure that the Xv attribute
exists before we set it (crash!).  Fix a silly float bug that
caused colorbalance to just not work.