For the palette mapping editor, problems were noticed when the threshold mode...

For the palette mapping editor, problems were noticed when the threshold mode was set to unlimited.  The range of values was set using the range of floating point numbers which caused problems with NaN sometimes being displayed and the sliders were not functioning.  Now, when the threshold is 'unlimited', the maximum absolute value for all date within the file is found.  For 'unlimited' the range is now (-2 * file-abs-max-value, 2 * file-abs-max-value)