Fixed crop program so it wipes out input cube after successive runs in the...

Fixed crop program so it wipes out input cube after successive runs in the GUI. Added more tests. Fixes #1500.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@5716 41f8697f-d340-4b68-9986-7bafba869bb8