shattering monster's weapon stack

Something I encountered while playing slash'em a while back, but
relevant to nethack:  "Its orcish spears shatter from the force of your
blow!".  I was using a two-handed weapon (at skilled or expert level) to
fight an invisible monster which was wielding a stack of multiple spears
(slash'em gives them out in groups of 3 for monsters' starting inventory).
After killing it, I found 2 orcish spears along with an invisible corpse
of somebody-or-other the Kobold King.  The message suggested that the
whole spear stack had been destroyed (and the weapon shattering code in
hmon_hitmon() clearly expects that to be the case), but only one of them
had actually gotten used up.

     I can't recall whether "shatter" was actually given as singular or
plural at the time; nethack handles that aspect correctly.  Only object
destruction needed tweaking.

include/extern.h

@@ -1358,6 +1358,7 @@ E int FDECL(breamu, (struct monst *,struct attack *));
 E boolean FDECL(linedup, (XCHAR_P,XCHAR_P,XCHAR_P,XCHAR_P));
 E boolean FDECL(lined_up, (struct monst *));
 E struct obj *FDECL(m_carrying, (struct monst *,int));
+E void FDECL(m_useupall, (struct monst *,struct obj *));
 E void FDECL(m_useup, (struct monst *,struct obj *));
 E void FDECL(m_throw, (struct monst *,int,int,int,int,int,struct obj *));
 E boolean FDECL(hits_bars, (struct obj **,int,int,int,int));