This change adds support for VP8 partitions in the video jitter buffer and
the VP8 encoder and decoder wrappers. The feature is currently disabled by
default since it requires a later version of libvpx.
With this change the jitter buffer will also start keeping track of each
packet header until decoding, and the VCMSessionInfo and VCMPacket objects
will keep pointers into the encoded frame buffers.
Review URL: http://webrtc-codereview.appspot.com/137021
git-svn-id: http://webrtc.googlecode.com/svn/trunk@558 4adac7df-926f-26a2-2b94-8c16560cd09d
