Fixed OS X build

-Now builds on OS X (when external libraries present)
-FLTK's GLUT triggers warnings so I've disabled them for now.
-Removed unneeded debug output
-Removed redundant layer of threading for calculating the medial axis
-Fixed crash caused by an uninitialized vertex attribute array.
-Added MacroEnv.h that moves some of the build environment macros out
of Global.h