Updated implementation of RadarVolume face and floor computation. Added some optimizations and minimum-elevation parameter to RadarVolumeExample.

git-svn-id: http://worldwind31.arc.nasa.gov/svn/trunk@2437 822214bb-dcf7-4c8d-a767-17ae0fb20d88
Corrected off-by-one error in RadarVolumeExample. Added some documentation to RadarVolume.

git-svn-id: http://worldwind31.arc.nasa.gov/svn/trunk@2438 822214bb-dcf7-4c8d-a767-17ae0fb20d88