FFmpeg version check changes

This pull will allow BigBlueButton to run properly with FFmpeg version 0.11.3.

I've actually removed the version check from the processing scripts completely, since the only version of FFmpeg that we really support in the BigBlueButton 0.81 release is 0.11.x (we use other features that don't work properly with older versions)

I've added an FFmpeg version check to `bbb-conf --check` so we have a more reliable way of ensuring that people meet the required ffmpeg version.

These changes have been tested on my local server using both ffmpeg 0.11.2 *and* 0.11.3, and recording processing works correctly with either.