Added libhb and CLI support for Dolby Pro Logic II 5.0 matrix encoding. *NOT YET...

Added libhb and CLI support for Dolby Pro Logic II 5.0 matrix encoding.  *NOT YET ADDED TO THE GUI*.  Handbrake now uses a more general "audio mixdown" concept.  For each audio track to be converted you specify a mixdown.  These are defined in common.h.
This checkin only allows you to specify one mixdown for all tracks in the CLI, although everything is in place internally to specify a different mixdown per track.  In the CLI, the "-6 --surround" option has been repurposed as a "-6 --mixdown" option, with a string parameter of mono/stereo/dpl1/dpl2/6ch.

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@494 b64f7644-9d1e-0410-96f1-a4d463321fa5