Fixed SubArea class so it recalculates the min/max lat/lon keyword values of...

Fixed SubArea class so it recalculates the min/max lat/lon keyword values of cropped maps with equatorial cylindrical projections. Fixes #1500.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@5714 41f8697f-d340-4b68-9986-7bafba869bb8