Added test for BandBin groups with keywords containing only one value. This...

Added test for BandBin groups with keywords containing only one value.  This test has been added to ensure the changes made in reference to issue #375 are tested, and the scenario is accounted for in the test suite.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@3109 41f8697f-d340-4b68-9986-7bafba869bb8