Made test to ensure every image overlaps another optional, and also fixed it...

Made test to ensure every image overlaps another optional, and also fixed it to account for images later in the list, and now prints out the name of the input cube that failed, not its output filename.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@3762 41f8697f-d340-4b68-9986-7bafba869bb8