bag of tricks, horn of plenty, #tip (trunk only)

<Someone> reported that he applied an unID'd bag and it became
discovered as a bag of tricks even though a spellbook appeared on the floor
next to him rather than having a monster show up (the monster was a mimic).
Suppress the bag discovery unless you can see or sense a monster appear.
(This doesn't really achieve much for most players, who'll recognize the
bag because they know that only one type of container doesn't prompt to
take things out and/or put things in, but I think it does make sense.)

     While mucking with bag of tricks I decided that to be consistent with
the behavior of other containers, the #tip command should release all the
monsters in the bag instead of just one.

     And after doing that, I realized that horn of plenty ought to behave
much the same, so #tip will operate on it now.  However, it won't be listed
as a likely candidate in the "which item?" prompt unless/until it has been
discovered.  (Attempting to empty any other type of horn yields "nothing
happens", same as for a horn of plenty with no charges left.)  Emptying a
horn of plenty in a shop can be extremely verbose, but I don't think that
qualifies as a bug and don't currently have any plans to alter it.

include/extern.h

@@ -1004,7 +1004,7 @@ E void FDECL(mimic_hit_msg, (struct monst *, SHORT_P));
 #ifdef GOLDOBJ
 E void FDECL(mkmonmoney, (struct monst *, long));
 #endif
-E void FDECL(bagotricks, (struct obj *));
+E int FDECL(bagotricks, (struct obj *,BOOLEAN_P));
 E boolean FDECL(propagate, (int, BOOLEAN_P,BOOLEAN_P));
 E boolean FDECL(usmellmon, (struct permonst *));
 
@@ -1168,6 +1168,7 @@ E void FDECL(add_to_buried, (struct obj *));
 E void FDECL(dealloc_obj, (struct obj *));
 E void FDECL(obj_ice_effects, (int, int, BOOLEAN_P));
 E long FDECL(peek_at_iced_corpse_age, (struct obj *));
+E int FDECL(hornoplenty, (struct obj *,BOOLEAN_P));
 #ifdef WIZARD
 E void NDECL(obj_sanity_check);
 #endif