Bring back support of FFmpeg >= 0.7

After planar codecs support minimal FFmpeg was
bumped to 0.10 which was not so much nice because
it was only released only later last year.

Didn't find a way to make compatibility code local
in ffmpeg_compat, so there're some ifdefs in
audaspace and writeffmpeg.

Not entirely happy, but having a bit of ifdefs in
code better than lots of real PITA for platform
maintainers.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56175 954f8c5b-7b00-dc11-b283-0030488c597c