add ability for a callback to abort a TimerCallback
add ability for a callback to abort a TimerCallback

manuelli/director,rdeits/director,gizatt/director,RobotLocomotion/director,manuelli/director,RobotLocomotion/director,RussTedrake/director,openhumanoids/director,mitdrc/director,gizatt/director,mithrandir123/director,rdeits/director,patmarion/director,RussTedrake/director,rdeits/director,mithrandir123/director,empireryan/director,mitdrc/director,empireryan/director,mitdrc/director,empireryan/director,empireryan/director,edowson/director,edowson/director,gizatt/director,RussTedrake/director,patmarion/director,rdeits/director,openhumanoids/director,gizatt/director,rdeits/director,mithrandir123/director,mithrandir123/director,gizatt/director,RobotLocomotion/director,RobotLocomotion/director,edowson/director,patmarion/director,edowson/director,mithrandir123/director,RussTedrake/director,manuelli/director,RobotLocomotion/director,manuelli/director,RussTedrake/director,mitdrc/director,patmarion/director,openhumanoids/director,manuelli/director,mitdrc/director,empireryan/director,openhumanoids/director,edowson/director,patmarion/director,openhumanoids/director