* Moved destruction of ReferenceCounted object to seperate thread (thus unloading rendering thread)
 * integration of OpenGL garbage collector into OpenGLJobProcessor (finally, you don't need to care anymore whether your code might call a GL object destructor and hence needs an OpenGL context)
 * changed DataContainer implementation from mutex/lock to concurrent container
 * fixing improper order of GL object deinitilization on program exit

git-svn-id: https://camplinux.in.tum.de/svn/campvis/trunk@492 bb408c1c-ae56-11e1-83d9-df6b3e0c105e