using #monster to breath at self (trunk only)

When testing the monster-breath-at-self patch I noticed that trying
to cure green slime by having hero breathe at self didn't work.  The code
was calling buzz() with arguments that produced an attack directed against
the hero's location, but there was a chance for it to miss outright and
when it didn't, reflection would block it.  This makes breathing at
yourself with `#monster' comparable to zapping a wand or casting a spell
at yourself:  it always hits.

include/extern.h

@@ -2624,6 +2624,7 @@ E int FDECL(zappable, (struct obj *));
 E void FDECL(zapnodir, (struct obj *));
 E int NDECL(dozap);
 E int FDECL(zapyourself, (struct obj *,BOOLEAN_P));
+E void FDECL(ubreatheu, (struct attack *));
 E boolean FDECL(cancel_monst, (struct monst *,struct obj *,
 			       BOOLEAN_P,BOOLEAN_P,BOOLEAN_P));
 E void FDECL(weffects, (struct obj *));