sparse_disp: add debugging options, catch bad-match errors

-Can now specify -D to get an output csv of disparity points, a second csv of points that have failed with an indication of why they failed, plus chit-chat from the script as it runs

-Errors where norm_xcorr returned 'None' were getting passed through as zero-disparity points.  These should have been deleted.
sparse_disp: change success criteria

1. increase teh default epipolar tolerance
2. allow the minimum maximum-disparity value  to be specified