In grid, Adam Licht added functionality to choose the source of image...

In grid, Adam Licht added functionality to choose the source of image background. Pixel Values for behind the grid can now be the image pixel value, HRS, LRS, NULL, or a DN. We incorporated Adam Licht's changes into Isis. This included re-formatting to match current Isis 3 coding standards, removal of error checking of conditions that cannot happen, fixes with running in batch mode/resetting of variable states between runs, some re-positioning of parameter locations, and creating tests. These changes shouldn't break any existing scripts that utilize grid. Fixes #917.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4946 41f8697f-d340-4b68-9986-7bafba869bb8