Fixed #250 by considering the longitude range 0-360 to mean the entire planet,...

Fixed #250 by considering the longitude range 0-360 to mean the entire planet, not 0-0.  Changed Latitude and Longitude classes to validate themselves within a given range, allowing for this added functionality outside of individual applications, and providing robust support for wrapping longitude values and double precision problems.  Latitude has been given a new constructor taking only an angle to accomodate this new method, IsInRange().  The Angle class has also been changed to provide a convenience != operator.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@2866 41f8697f-d340-4b68-9986-7bafba869bb8