PROG Fixed broken cnetedit fix so that reference measures are correctly...

PROG Fixed broken cnetedit fix so that reference measures are correctly deleted when in a MEASURELIST and DELETE=YES. Also updated documentation and added another test. Fixes #2238

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@6311 41f8697f-d340-4b68-9986-7bafba869bb8