- (void) append:(OBPerform *)perform
appends a new perform invocation to the queue
- (void) cancelWithPerform:(OBPerform *)perform
cancels this exact perform instance
- (void) cancelWithSelector:(SEL)selector
- (void) cancelWithSelector:(SEL)selector target:(id)target
- (void) cancelWithTarget:(id)target
- (void) perform
performs all queued invocations