[mythtv] ffmpeg pull requests

[Scott Theisen]

av_disposition: https://github.com/MythTV/mythtv/pull/575 and 
https://github.com/MythTV/FFmpeg/pull/5 or first commit in 
https://github.com/MythTV/FFmpeg/pull/4 (which uses the new `#define`)

lavc/utils-mythtv: https://github.com/MythTV/mythtv/pull/565 the changes 
to FFmpeg are already merged to FFmpeg/master, but I can redo it to make 
the minimal changes to FFmpeg if desired.

MythTV only changes:
https://github.com/MythTV/mythtv/pull/557 ByteReader
https://github.com/MythTV/mythtv/pull/577 BitReader (depends on/includes 
ByteReader)
https://github.com/MythTV/mythtv/pull/576 Miscellaneous MythTV changes

After those and the rest of the changes to FFmpeg are merged into 
MythTV, the harmonize commits can be tested, particularly with 
DSMCC/MHEG which I don't have access to. 
https://github.com/MythTV/mythtv/pull/524 corresponds to 
https://github.com/MythTV/FFmpeg/pull/4 note: 
https://github.com/MythTV/mythtv/pull/524/commits/323e3ddaa4ac9acced65d9826908f41a1360932d

Regards,

Scott