Add and test --[no]check-child-tables.

t/pt-table-sync/samples/on_del_cas.sql

@@ -0,0 +1,19 @@
+DROP DATABASE IF EXISTS on_del_cas;
+CREATE DATABASE on_del_cas;
+USE on_del_cas;
+
+CREATE TABLE parent (
+  id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
+) ENGINE=InnoDB;
+
+CREATE TABLE child1 (
+  id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  parent_id INT NOT NULL,
+  FOREIGN KEY fk1 (parent_id) REFERENCES parent (id) ON DELETE RESTRICT
+) ENGINE=InnoDB;
+
+CREATE TABLE child2 (
+  id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  parent_id INT NOT NULL,
+  FOREIGN KEY fk1 (parent_id) REFERENCES parent (id) ON DELETE CASCADE
+) ENGINE=InnoDB;