speedup of getAlternativeLabels in DistanceToleranceFunction: stop iterating in neighborhood if all currently tracked labels have been found
yet another speed-up :) : reordered neighborhood to foster early iteration break
made DistanceToleranceFunction background label aware
changed tolerance criterion to <= (was <) in DistanceToleranceFunction
made DistanceToleranceFunction less verbose
select fewer boundary pixels in DistanceToleranceFunction (only "4"-neighborhood)
added slight background preference to TolerantEditDistance (doesn't change error measure, but looks nicer)