unpaid tinning kit usage

<Someone> reported that shopkeepers don't charge for using tinning kits.

doc/fixes34.2

@@ -36,6 +36,7 @@ some Magicbane messages treated "erinys" as plural
 initialize artifacts before processing $WIZKIT
 clean up inconsistency between various places quaff is documented
 is_damageable was using is_rottable incorrectly
+charge for use of an unpaid tinning kit
 
 
 Platform- and/or Interface-Specific Fixes

src/apply.c

@@ -1408,6 +1408,7 @@ register struct obj *obj;
 		pline("That's too insubstantial to tin.");
 		return;
 	}
+	check_unpaid(obj);
 	obj->spe--;
 	if ((can = mksobj(TIN, FALSE, FALSE)) != 0) {
 	    static const char you_buy_it[] = "You tin it, you bought it!";

src/shk.c

@@ -3849,7 +3849,8 @@ boolean altusage; /* some items have an "alternate" use with different cost */
 		if (otmp->spe > 1) tmp /= 4L;
 	} else if (otmp->oclass == SPBOOK_CLASS) {
 		tmp -= tmp / 5L;
-	} else if (otmp->otyp == CAN_OF_GREASE
+	} else if (otmp->otyp == CAN_OF_GREASE ||
+		   otmp->otyp == TINNING_KIT
 #ifdef TOURIST
 		   || otmp->otyp == EXPENSIVE_CAMERA
 #endif