Sensor.h: 2006-09-07 Debbie A. Cook - Changed back-of-planet test to use

Sensor.h: 2010-09-15 Janet Barrett - Modified the SetLookDirection method to use a new algorithm for finding the intersection of a ray with the DEM. This was required to take care of problems that 
Sensor.h: 2011-02-08 Jeannie Walldren - Added method parameter documentation. 

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@1703 41f8697f-d340-4b68-9986-7bafba869bb8