profiles/dv_*, consumer_avformat.c, producer_avformat.c: bugfix (1912796) to override...

profiles/dv_*, consumer_avformat.c, producer_avformat.c: bugfix (1912796) to override FFmpeg notion of sample aspect for DV. The values it uses might be more proper in certain contexts, but not in the way MLT currently operates. This change improves performance and quality when outputting to one of the "dv" profiles when using DV or other ITU-R 601-based video sources such as MPEG-2 for DVD Video and broadcast.

git-svn-id: https://mlt.svn.sourceforge.net/svnroot/mlt/trunk/mlt@1126 d19143bc-622f-0410-bfdd-b5b2a6649095