avoid "It turns into it"

<Someone> drew attention to the silly message in the newsgroup

Since I'm not sure if the act of polymorphing has a sound,
I opted to use a new usmellmon() routine to put out a
message based on the smell of the resulting monster
under those circumstances.

Not every monster has a recognizable smell, so no
message at all is given in that case.

olfactory(youmonst.data) will determine whether
you are capable of detecting smells.

There is lots of room for enhancement, and some of the
existing smell-related messages in the source should perhaps
be checking olfactory(youmonst.data) too, but this patch
doesn't go that far.

include/extern.h

@@ -973,6 +973,7 @@ E void FDECL(mkmonmoney, (struct monst *, long));
 #endif
 E void FDECL(bagotricks, (struct obj *));
 E boolean FDECL(propagate, (int, BOOLEAN_P,BOOLEAN_P));
+E boolean FDECL(usmellmon, (struct permonst *));
 
 /* ### mapglyph.c ### */
 
@@ -1223,6 +1224,7 @@ E const char *FDECL(locomotion, (const struct permonst *,const char *));
 E const char *FDECL(stagger, (const struct permonst *,const char *));
 E const char *FDECL(on_fire, (struct permonst *,struct attack *));
 E const struct permonst *FDECL(raceptr, (struct monst *));
+E boolean FDECL(olfaction, (struct permonst *));
 
 /* ### monmove.c ### */