DVDAudioCodecFFmpeg: Convert unknown audio formats to float.

As of FFmpeg-1.1, some decoders started to output planar audio.
This fixes track ticket 13944.
[IOS] - fix build after 6095130a0a441fdf61fa9ba1d1432ece3f5bc6a4
fixed: Missing build dep for libtiff-dev to the Linux/Ubuntu README docs
[touched] - revert unwanted submodule downgrade
Merge pull request #2117 from aballier/unknownaudioout

DVDAudioCodecFFmpeg: Convert unknown audio formats to float.