Implemented reference measure detection differently to work around problems...

Implemented reference measure detection differently to work around problems with PvlContainers HasKeyword method (PvlContainer will get fixed eventually.  This is not really a bad workaround.  This solution without using the HasKeyword method is just as clean)

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@1744 41f8697f-d340-4b68-9986-7bafba869bb8