Upgrade of the geom classes by Andrei:

- improvements in the drawing mechanism (nodes can also be made
invisible, having higher priority than volumes;
- possibility of simple phi cut in TGeoManager::SetPhiRange(phimin, phimax)
  - by default the phi range is (0, 360) - no cut performed
 - setting different values for phimin, phimax will make invisible the
nodes having the origin in this range;

- documentation updated for TGeoArb8 class (picture in /gif directory)


git-svn-id: http://root.cern.ch/svn/root/trunk@5443 27541ba8-7e3a-0410-8455-c3a389f83636