BUG/MAJOR: lua: use task_wakeup() to properly run a task once

The Lua tasks registered vi core.register_task() use a dangerous
task_schedule(task, now_ms) to start them, that will most of the
time work by accident, except when the time wraps every 49.7 days,
if now_ms is 0, because it's not valid to queue a task with an
expiration date set to TICK_ETERNITY, as it will fail all wakeup
checks and prevent all subsequent timers from being seen as expired.
The only solution in this case is to restart the process.

Fortunately for the vast majority of users it is extremely unlikely
to ever be met (only one millisecond every 49.7 days is at risk), but
this can be systematic for a process dealing with 1000 req/s, hence
the major tag.

The bug was introduced in 1.6-dev with commit 24f335340 ("MEDIUM: lua:
add coroutine as tasks."), so the fix must be backported to all stable
branches.

src/hlua.c

@@ -8268,7 +8268,7 @@ static int hlua_register_task(lua_State *L)
 	hlua->nargs = 0;
 
 	/* Schedule task. */
-	task_schedule(task, now_ms);
+	task_wakeup(task, TASK_WOKEN_INIT);
 
 	return 0;