* a worker thread puts every new task into a "pending" queue immediately after accepting it
* the "pending" check is checked regularly for old items -> they are reinjected into the task queue
* the risk of losing a task is now close to zero


git-svn-id: https://pycam.svn.sourceforge.net/svnroot/pycam/trunk@949 bbaffbd6-741e-11dd-a85d-61de82d9cad9