manager: order idle jobs

Let's put the run queue really the last spot, as we should only start
doing more work if we really have nothing else to do anymore.

Let's move the service watchdog after the rewatch PID logic for similar
logic: it will possibly result in new jobs being enqueued to stop
things, and we should really have done all other work first.

src/core/manager.h

@@ -662,7 +662,7 @@ enum {
         EVENT_PRIORITY_TIME_ZONE        = SD_EVENT_PRIORITY_NORMAL-1,
         EVENT_PRIORITY_IPC              = SD_EVENT_PRIORITY_NORMAL,
         EVENT_PRIORITY_REWATCH_PIDS     = SD_EVENT_PRIORITY_IDLE,
-        EVENT_PRIORITY_RUN_QUEUE        = SD_EVENT_PRIORITY_IDLE,
-        EVENT_PRIORITY_SERVICE_WATCHDOG = SD_EVENT_PRIORITY_IDLE,
+        EVENT_PRIORITY_SERVICE_WATCHDOG = SD_EVENT_PRIORITY_IDLE+1,
+        EVENT_PRIORITY_RUN_QUEUE        = SD_EVENT_PRIORITY_IDLE+2,
         /* … to least important */
 };