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

src/polyself.c

@@ -590,7 +590,7 @@ break_armor()
 	}
 #endif
     } else if (sliparm(youmonst.data)) {
-	if ((otmp = uarm) != 0) {
+	if (((otmp = uarm) != 0) && (racial_exception(&youmonst, otmp) < 1)) {
 		if (donning(otmp)) cancel_don();
 		Your("armor falls around you!");
 		(void) Armor_gone();