Measures no longer know or care if they are the reference measure. This...

Measures no longer know or care if they are the reference measure.  This information is now completely maintained by the ControlPoint class.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@1738 41f8697f-d340-4b68-9986-7bafba869bb8