X3D is displayed. Also removed the eventloop from X3D and put under
control of the ROOT event loop. Currently only one X3D viewer can be
open (due to several globals in the old X3D code). Protection still to
be added.


git-svn-id: http://root.cern.ch/svn/root/trunk@766 27541ba8-7e3a-0410-8455-c3a389f83636