In SunShadowTool, corrected the equation, in the recalculateShadowHeight()...

In SunShadowTool, corrected the equation, in the recalculateShadowHeight() method, that finds the height of the object casting the shadow. It now uses the tangent of the angle multiplied by the length of the shadow instead of the sine of the angle. Fixes #1933.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@5710 41f8697f-d340-4b68-9986-7bafba869bb8