HOWTO sync to a new ffmpeg CVS date:

a) manually update with cvs update -D 'new date tag'
b) fix stuff so that our plug-in builds against it
c) in configure.ac, replace the date tag with your new tag
d) copy gst-libs/ext/ffmpeg/ffmpeg/CVS/Tag to gst-libs/ext/ffmpeg/Tag
e) commit all these changes to cvs

The reason both c) and d) need to be done is because cvs doesn't understand
it's own Tag file format as a date spec.