Minor code cleanup.
Created the capability to directly compare two ranges. Currently draws
simple bar graphs with 1 std dev error bars, hardcoded to blue and
green.  To execute,"CompareRanges.py [filenamelist1] : [filenamelist2]".
Add a few math safeguards.
Minor option tweak.
Move filter_vagprops_for_graphing to Graphing.py so it can be used both
by CompareRanges.py and CompareToRange.py.