In the Longitude class, force360Domain() was modified so that if the angle is...

In the Longitude class, force360Domain() was modified so that if the angle is 360, it is left at 360 instead of being changed to 0. Added a test case to the unit test to exercise this change. Fixes #999.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4602 41f8697f-d340-4b68-9986-7bafba869bb8