Fixed an error with cam2map when matchmap was true, the user could add a...

Fixed an error with cam2map when matchmap was true, the user could add a mappingfile with a targetname that did not match the targetname in the instrument group of the cube file. Fixes #1952.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@6881 41f8697f-d340-4b68-9986-7bafba869bb8