LightTimeCorrection - Fixed test for light time correction request; cleaned up...

LightTimeCorrection - Fixed test for light time correction request; cleaned up vector computations in surface light time compensation.  References #1136.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4821 41f8697f-d340-4b68-9986-7bafba869bb8