Updated MosaicSceneItem to work with a longitude domain of 180 correctly, so...

Updated MosaicSceneItem to work with a longitude domain of 180 correctly, so qmos will display footprints crossing the -180/180 boundary correctly. Fixes #2208

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@6205 41f8697f-d340-4b68-9986-7bafba869bb8