optimize one more draw call

git-svn-id: svn://svn.code.sf.net/p/vpinball/code/trunk@890 14438d79-0ffd-4333-8ae7-ea2bdd901387
Some comments and small fixes for 3D math.
Another fix to CMake file.
Refactored check for habitrails into its own method.
Merge branch 'fixes' of https://github.com/c-f-h/vpinball into fixes