removed a glReadBuffer(GL_FRONT); statement that may cause an error if there is no double buffering
removed a glReadBuffer(GL_FRONT); statement that may cause an error if there is no double buffering

git-svn-id: 83c4c97093aeea62ac982fbfd516bf9db27f5c99@1946 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok