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.

include/extern.h

@@ -1940,7 +1940,7 @@ E void FDECL(domagicportal, (struct trap *));
 E void FDECL(tele_trap, (struct trap *));
 E void FDECL(level_tele_trap, (struct trap *));
 E void FDECL(rloc_to, (struct monst *,int,int));
-E void FDECL(rloc, (struct monst *));
+E boolean FDECL(rloc, (struct monst *, BOOLEAN_P));
 E boolean FDECL(tele_restrict, (struct monst *));
 E void FDECL(mtele_trap, (struct monst *, struct trap *,int));
 E int FDECL(mlevel_tele_trap, (struct monst *, struct trap *,BOOLEAN_P,int));