SubArea.h: 2011-01-24 Steven Lambright - Cameras are still valid when linc and...

SubArea.h: 2011-01-24 Steven Lambright - Cameras are still valid when linc and sinc are not equal, so now this class is more likely to not delete the instrument group. 

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@1599 41f8697f-d340-4b68-9986-7bafba869bb8