While the FFmpeg video IO backend gets compiled even without it,
the tests (for both FFmpeg and video IO) don't. This should fix
that.

folowing additional options: --enable-w32threads, --arch=i686 (for 32-bit
library, workaround for http://trac.ffmpeg.org/ticket/2363)

get back to single-version ffmpeg wrapper (no more v2); make sure the library builds and the tests pass on Ubuntu 10.04 that includes pretty old version of ffmpeg

added key frame handling to ffmpeg wrappers