ffmpeg backport: VC-1 DXVA2 improvements / Intel compat

As an alternative to #4204, here's a backport of the Jan.1 2014 ffmpeg VC1 fixes which affect DXVA decoding mainly on Intel HW. I tested with all VC1 material I have (which isn't an awful lot) on Intel HD 4600 GPU. Probably needs more testing on other hardware.

This PR contains the following ffmpeg commits:
8abdf46b380562d4716a78174076b1e67ae1f8da dxva2_vc1: set refdist value according to spec
3021d1be9ef1f863f880b5c667025936b45da065 dxva2_vc1: set bfraction in slice info according to spec
e1facd3f8198fc4bfd54f3a4097e66513e6bf3e4 dxva2_vc1: set PQUANT as described by the 2010 spec update
719f1ce5fb41493fe10edca1ba9223fa601b6165 vc1: set chromaformat = 1 for simple/main profile
c5562890c7c3e495a1995bfa64f730806020e8d6 dxva2_vc1: fix signaling of intensity compensation values
3d8eeea62009a85c88ee4a630da4d6037920aa6e dxva2_vc1: signal skipped p frames

Here's the original post from the ffmpeg mailing list:
http://lists.ffmpeg.org/pipermail/ffmpeg-devel/2013-December/151913.html