GetLabels() returns a vector of labeled regions. The largest one is the entire
image, and the second-largest one is the region we want to crop. The code was
assuming that the regions were returned in order of size, but we found a movie
where that wasn't the case. So now we look at all the regions, compute all
their areas, and use the one that's second-biggest.

Working-ish version of reseg code. Also, new version of mexDijkstra supports searching "through" terminal vertices.

Modified GetTrackingCosts and associated mex code to use a passed-in connected-component distance structure instead of the global ConnectedDist variable.

The idea behind this is to prevent a race condition in LEVer where it starts
processing the segmentation file before HematoSeg.exe has finished writing it
all out. So when the thread has written the entire file and closed it, we now
create a new 0-byte semaphore file to indicate that it's OK for LEVer to
process it. In case the segmentation gets run more than once, we delete all of
the semaphore files for this movie in the initialization code, before the
threads start running.

Previously we were only doing this for thresholdOrg, but for the Naik UBC
movies it's necessary for the grayscale Otsu as well.

Always reference count tracks and hulls in integrity check even if there are errors in the family or track.

Updated integrity check to give slightly clearer error messages and to avoid spurious reference errors.

FixOldFileVersions will initialize HashedCells to an empty structure if there are no cells in frame.

MexIntegrityCheck now handles empty (non-structured) HashedCells entries, and produces an error.

Make mexDijkstra (checkExtension) search ignore user-edited mitosis events when considering possible inference extensions.

Cost function returns a minimum of costEpsilon > 0. Fixes rare case when cost function evaluates to zero, which appears to be an infinite cost edge in matlab.