Fix several touchstone-related things:

1. The switch statement was using the material "GOLD"
   rather than GOLD_CLASS.
2. If getobj() had been working for gold when it
   came to touchstones, there would have been a
   memory leak here because the object returned
   would have been from mkgoldobj().  The goldobj
   was not being freed anywhere, nor was it being
   put on a chain. You also would have had zero
   gold after rubbing it on the stone. The intent
   was clearly to allow gold since there was a
   case in the switch statement.
3. getobj() wasn't working properly for gold
   selection here anyway, so this was
   not the cause of <Someone>'s gold obj in inventory.
   You ended up dropping through to code that
   was supposed to print "You cannot verb object."
   For touchstones that came out as:
   "You cannot rub on the stone gold."

src/invent.c

@@ -729,6 +729,10 @@ register const char *let,*word;
 #else
 	if(*let == GOLD_CLASS) let++, usegold = TRUE;
 #endif
+	/* Ugly check for touchstone */
+	if (!strncmp(word, "rub on", 6) && u.ugold)
+		allowgold = usegold = TRUE;
+
 	/* Equivalent of an "ugly check" for gold */
 	if (usegold && !strcmp(word, "eat") && !metallivorous(youmonst.data))
 #ifndef GOLDOBJ