buglist entry: hobbits and elven mithril armour

<Someone> wrote: "Also, hobbits can't wear armour,
at least, you can't wear armour when polymorphed into a hobbit, even
though hobbits do tend to be carrying elven mithril-coats.
It's tempting to suggest adding an explicit exception in
sliparm() for elven mithril just to keep the Tolkienness."

- added a general routine for adding race-based /object
combination exceptions.
- hobbits can wear elven mithril-coats

include/extern.h

@@ -2287,6 +2287,7 @@ E struct obj *FDECL(which_armor, (struct monst *,long));
 E void FDECL(mon_break_armor, (struct monst *,BOOLEAN_P));
 E void FDECL(bypass_obj, (struct obj *));
 E void NDECL(clear_bypasses);
+E int FDECL(racial_exception, (struct monst *, struct obj *));
 
 /* ### write.c ### */