Fix MV rate updates in the refinement DP.

od_mv_dp_get_rate_change() was not following the path back through
 the trellis properly.
It was using the state of the last node in the trellis to look up
 the previous state at every node, rather than the actual state at
 that node.

Thanks to Guillaume Martres for the bug report.
Clean-up some hard-coded constants.

Give names to various sizes so it's clear where they come from and
 when they might need to be changed.
Clean up some MC logging issues.

Don't dump a log message for every SAD computation.
Make the buffer overflow check in od_mv_dp_get_rate_change() assert
 instead of logging at the OD_LOG_DEBUG level.
Print lambda instead of lambda*8 (the extra *8 was just there for
 comparison with the old lambda values before commit 713cde8f4fd3).
Remove edge labels from MV grid.

Just continuing to remove code that is now unused since CGI was
 removed.
Remove obsolete MC test code.

This was designed to test continuity between the various edge
 interpolation types.
Since we no longer support CGI, there is only one edge type.
Technically, we could still repurpose this test to check for
 continuity between OBMC blending when adjacent block sizes differ,
 but that would require redesigning the test, and would have to be
 reworked when support for adjacent blocks that differ by more than
 one size level is added.
Fix a typo in the mesh decimation description.

v is only used in the sense of "for all v".
The specific v being operated on throughout step 2 is v^*.

Thanks to Guillame Martres for the report.