- changed the main INCLUDE_DIRECTORIES definition to place the main header

- changed the main INCLUDE_DIRECTORIES definition to place the main header
  locations first in the list instead of appending them. This gives priority to
  our freeglut*.h files instead of the old system-wide installed ones.
- removed the Xxf86vm hack from CMakeLists.txt: it seems like it's not needed
  any more in new versions of cmake, and it fails to link on MacOSX.

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@1745 7f0cb862-5218-0410-a997-914c9d46530a