in revision 1.40 is clearly incorrect. If the cleaner is already in the busy state, a call to
incremental_cleaning_action() has already been scheduled as an event, and there is no
need to do an extra call. Furthermore, the call passed the timer event as an argument
to incremental_cleaning_action(), which would ultimately cause it to be passed
to end_cleanin() and assigned to cleaner->resched_event rather than freed.
This commit may or may not fix RT #1912.
937ccb270e