Added new method, SpacecraftSurfaceVector, which returns the spacecraft to...

Added new method, SpacecraftSurfaceVector, which returns the spacecraft to surface point vector in body-fixed.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@3822 41f8697f-d340-4b68-9986-7bafba869bb8