Add segmentation map to Decoder
Thread (mutable) segmentation map to macroblock header constructor
Maintain persistent macroblock segmentation map
Correct wraparound in quantization settings
decode-to-stdout.cc: correct treatment of non-integral macroblock height
macroblock.cc: Fix assertion failure when prob_skip_false not present
Correct semantics of segment adjustments to filter/quantizer
loopfilter.cc: Add parens to fix loopfilter segment adjustment
Simplify treatment of segment adjustments
Even a keyframe can decide not to refresh entropy probs. Now passes all conformance tests!