Fix for 1003315: dry-run + alter-fk-method = auto always fail.

t/pt-online-schema-change/samples/bug-1003315.sql

@@ -0,0 +1,23 @@
+drop database if exists test1003315;
+create database test1003315;
+use test1003315;
+
+DROP TABLE IF EXISTS `B`;
+DROP TABLE IF EXISTS `A`;
+CREATE TABLE `A` (
+  `id` int(11) NOT NULL AUTO_INCREMENT,
+  `foo` varchar(30) NOT NULL,
+  PRIMARY KEY (`id`)
+) ENGINE=InnoDB;
+
+DROP TABLE IF EXISTS `B`;
+CREATE TABLE `B` (
+  `id` int(11) NOT NULL AUTO_INCREMENT,
+  `a` int(11) NOT NULL,
+  KEY `9dde1f34` (`a`),
+  PRIMARY KEY (`id`),
+  CONSTRAINT `6970ddb42bec57fc` FOREIGN KEY (`a`) REFERENCES `A` (`id`)
+) ENGINE=InnoDB;
+
+INSERT INTO `A` VALUES (1,'bar'), (2,'bar2'), (3,'bar3');
+INSERT INTO `B` VALUES (1, 1), (2, 2), (3, 1);