1) cosmetic change, no reason these need to be mpeg2-specific
2) add a flag to tell when fields are ordered, so we don't have to
assume bff (which would usually be wrong) when field flags are not
available.
3) add other flags for future use :)
git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@10664 b3059339-0415-0410-9bf9-f77b7e298cf2