Show cost of merchandise when walking over it

This is another feature the betatesters seemed to miss a lot.

src/shk.c

@@ -1865,6 +1865,36 @@ unsigned id;
     return (struct obj *) 0;
 }
 
+/* Returns the price of an arbitrary item in the shop.
+ * Returns 0 if the item doesn't belong to a shopkeeper. */
+long
+get_cost_of_shop_item(obj)
+register struct obj *obj;
+{
+    struct monst *shkp;
+    xchar x, y;
+    int cost=0;
+
+    if (get_obj_location(obj, &x, &y, 0) &&
+        (obj->unpaid ||
+         (obj->where == OBJ_FLOOR && !obj->no_charge && costly_spot(x,y)))) {
+
+        if (!(shkp = shop_keeper(*in_rooms(x, y, SHOPBASE)))) return 0;
+        if (!inhishop(shkp)) return 0;
+        if (!costly_spot(x, y))	return 0;
+        if (!*u.ushops) return 0;
+
+        if (obj->oclass != COIN_CLASS) {
+            cost = (obj == uball || obj == uchain) ? 0L :
+                obj->quan * get_cost(obj, shkp);
+            if (Has_contents(obj)) {
+                cost += contained_cost(obj, shkp, 0L, FALSE, FALSE);
+            }
+        }
+    }
+    return cost;
+}
+
 /* calculate the value that the shk will charge for [one of] an object */
 STATIC_OVL long
 get_cost(obj, shkp)