Event loop: call after sleep() only from top level.

In general we do not want before/after sleep() callbacks to be called
when we re-enter the event loop, since those calls are only designed in
order to perform operations every main iteration of the event loop, and
re-entering is often just a way to incrementally serve clietns with
error messages or other auxiliary operations. However, if we call the
callbacks, we are then forced to think at before/after sleep callbacks
as re-entrant, which is much harder without any good need.

However here there was also a clear bug: beforeSleep() was actually
never called when re-entering the event loop. But the new afterSleep()
callback was. This is broken and in this instance re-entering
afterSleep() caused a modules GIL dead lock.

src/ae.h

@@ -46,6 +46,7 @@
 #define AE_TIME_EVENTS 2
 #define AE_ALL_EVENTS (AE_FILE_EVENTS|AE_TIME_EVENTS)
 #define AE_DONT_WAIT 4
+#define AE_CALL_AFTER_SLEEP 8
 
 #define AE_NOMORE -1
 #define AE_DELETED_EVENT_ID -1