Threshold dialog exhibits roundoff errs

The min and max values in the threshold dialog can be manipulated with the dark background button. When you do so the min/max cutoffs are succeptible to rounding issues due to calculating from bottom..cutoff and cutoff+1 .. top. The +1 here is done before scaling. The real effect is likely a nonissue but it looks bad. Perhaps when the image is of integral type the min/max values should always be rounded to integers.

Migrated-From: http://trac.imagej.net/ticket/1684

Reproduce the issue by manipulating the min and max values with the threshold dialog's dark background button, then trace how the bottom, cutoff, and top values are calculated and scaled. Done means integral images show integer min/max cutoffs without visible rounding artifacts.

Written by the indexing model from the issue text.