sched: add function to remove all timers and descriptors

This allows a helper process to be started in an *_Initialise() call
and use the scheduler (unlike the privops helper, which has its own
loop).

sched.h

@@ -82,6 +82,9 @@ extern SCH_TimeoutID SCH_AddTimeoutInClass(double min_delay, double separation,
 /* The next one probably ought to return a status code */
 extern void SCH_RemoveTimeout(SCH_TimeoutID);
 
+/* Remove all timeouts and close all file descriptors */
+extern void SCH_Reset(void);
+
 extern void SCH_MainLoop(void);
 
 extern void SCH_QuitProgram(void);