CTXCamera: fixed bug with images that have SpatialSumming=2, they were...

CTXCamera: fixed bug with images that have SpatialSumming=2, they were compressed in the y-direction.  The lineRate was not being calculated correctly.  Fixes # 826

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4938 41f8697f-d340-4b68-9986-7bafba869bb8