improve pano matching

1.) Let ransac use inlier set cardinality as fitness function.
2.) When refitting with inliers, use all inliers instead of just first 4.

About 2s slower.
use regular ransac: only refit model at the end

Recovers 2s slowdown from last CL and more: pano program now runs in 8s
instead of 9s compared to before last CL (and 13s with the last CL).
implement msac. does not seem better or worse in pano demo.
measure pano time, cache match result (took 3s). pano now runs in 4s.