Fix for Judith hopefully

It has been determined that on certain platforms and for reasons not fullyunderstood that double buffering screws up the display of gmex so that one sees nothing, not even a black empty gl window. This has been the case thus far on platforms with Intel graphics. The solution is a little crude: only if the NVIDIA driver is detected to we enable double buffering. For the MAC platform we do not check and always use double buffering since that does not cause problems on the mac.