Fix bug #5814 - Winbindd dumping core in a strange manner while doing "rescan_trusted_domain".

From analysis by hargagan <shargagan@novell.com> :
"The winbindd_child_died() is also getting called from process_loop() in case of
SIGCHLD signal. In this case it doesn't make the timeout_handler to NULL for
the first request. It then initiate a new request using
schedule_async_request() which installs a new timeout handler for the same
request. In such a case, for a badly unresponsive system both the timeout
handler can be called. For the first call the "private_data" will be cleared
and for another call the timeout handler will be detecting the double free. So,
for such a case as well, the winbindd_child_died() should make the
timeout_handler to NULL."
Jeremy.

source3/winbindd/winbindd_dual.c

@@ -300,6 +300,18 @@ static void schedule_async_request(struct winbindd_child *child)
 		return;		/* Busy */
 	}
 
+	/*
+	 * This may be a reschedule, so we might
+	 * have an existing timeout event pending on
+	 * the first entry in the child->requests list
+	 * (we only send one request at a time).
+	 * Ensure we free it before we reschedule.
+	 * Bug #5814, from hargagan <shargagan@novell.com>.
+	 * JRA.
+	 */
+
+	TALLOC_FREE(request->reply_timeout_event);
+
 	if ((child->pid == 0) && (!fork_domain_child(child))) {
 		/* fork_domain_child failed.
 		   Cancel all outstanding requests */
@@ -495,6 +507,17 @@ void winbind_child_died(pid_t pid)
 	child->event.flags = 0;
 	child->pid = 0;
 
+	if (child->requests) {
+		/*
+		 * schedule_async_request() will also
+		 * clear this event but the call is
+		 * idempotent so it doesn't hurt to
+		 * cover all possible future code
+		 * paths. JRA.
+		 */
+		TALLOC_FREE(child->requests->reply_timeout_event);
+	}
+
 	schedule_async_request(child);
 }