added another OpenGL setting ("use caching") - this should solve the problem reported by a Windows user:
* http://sourceforge.net/tracker/index.php?func=detail&aid=3465407&group_id=237831&atid=1104176


git-svn-id: https://pycam.svn.sourceforge.net/svnroot/pycam/trunk@1226 bbaffbd6-741e-11dd-a85d-61de82d9cad9