buglist - full level triggers impossible() from migrating mons

<email deleted> wrote:
> If more monsters fall through a trap door than can fit on the
> level below, when you go down the stairs, you get the following
> message:
>  "Program in disorder - perhaps you'd better #quit.
>  rloc(): couldn't relocate monster"
> This message seems to appear once for every monster-too-many that
> fell through the hole. I originally found this while
> intentionally completely filling a level with black puddings
> (there was a trap door I didn't know about). I also confirmed it
> in a wiz-mode test using gremlins and water.

[confirmed: moveloop -> deferred_goto -> goto_level ->
 losedogs -> mon_arrive -> rloc -> impossible]

This patch:
- causes rloc() to return TRUE if successful,
  or FALSE if it wasn't.
- adds code to mon_arrive() in dog.c to deal with
  the failed rloc()
- allows the x,y parameters to mkcorpstat() to
  be 0,0 in order to trigger random placement of the
  corpse on the level
- if you define DEBUG_MIGRATING_MONS when you build cmd.c
  then you'll have a debug-mode command #migratemons to
  store the number of random monsters that you specify
  on the migrating monsters chain.

src/dig.c

@@ -59,7 +59,7 @@ mkcavepos(x, y, dist, waslit, rockit)
 	if(IS_ROCK(lev->typ)) return;
 	if(t_at(x, y)) return; /* don't cover the portal */
 	if ((mtmp = m_at(x, y)) != 0)	/* make sure crucial monsters survive */
-	    if(!passes_walls(mtmp->data)) rloc(mtmp);
+	    if(!passes_walls(mtmp->data)) (void) rloc(mtmp, FALSE);
     } else if(lev->typ == ROOM) return;
 
     unblock_point(x,y);	/* make sure vision knows this location is open */