Added ability to apply a gradient filter to chips before attempting to perform...

Added ability to apply a gradient filter to chips before attempting to perform a match. Renamed member variables to be consistent with the variable naming scheme in the rest of the file.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@1984 41f8697f-d340-4b68-9986-7bafba869bb8