will accept incorrect pix_fmt's and such, but decoder will work much better
with containers not setting the same attributes. It seems like there will
be a generic mechanism for checking such constraints, but if not I can always
resurrect this check for *encoder* only.


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@5114 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b