1. TGLTube replaced by TGLCylinder - generic class for tubes, cones,
segments and cuts (in theory, for polycones too). Tubes are drawn now as
strips (quad and triangle), real normals for tubes are calculated.
gl vertex arrays are used.
2. For each type of tube, I know the exact size of vertices arrays I need
- I don't need to use nsegments (because of real normals, we don't need
large tube segmentation to get smooth surfaces).


git-svn-id: http://root.cern.ch/svn/root/trunk@10952 27541ba8-7e3a-0410-8455-c3a389f83636