Prevent the user to close a canvas while the threads are running
Prevent the user to close a canvas while the threads are running


git-svn-id: ecbadac9c76e8cf640a0bca86f6bd796c98521e3@37739 27541ba8-7e3a-0410-8455-c3a389f83636

dawehner/root,dawehner/root,dawehner/root,dawehner/root,dawehner/root,dawehner/root,dawehner/root,dawehner/root