Improve reference ordering in interleaved 3D video

Improve reference ordering in interleaved 3D video
 Provides a decent compression improvement when encoding interleaved 3D content (--frame-packing 5).
 Helps more without B-frames and at lower bitrates.
 Note that x264 will not do this optimization unless --frame-packing 5 is used to tell x264 that the source is interleaved 3D.

Tests consistently show that interleaved frame packing is by far the best way to compress 3D content.
It gives a ~35-50% compression benefit over separate streams or top/bottom or left/right coding.

Also finally add support for L1 reference reordering (in B-frames).
Also add support for reordered ref0 in L0 and L1 lists; could be useful in the future for other things.