Add `generateChangeScript()` back

lib/private/db/mdb2schemamanager.php

@@ -95,6 +95,15 @@ class MDB2SchemaManager {
 		}
 	}
 
+	/**
+	 * @param \Doctrine\DBAL\Schema\Schema $schema
+	 * @return string
+	 */
+	public function generateChangeScript($schema) {
+		$migrator = $this->getMigrator();
+		return $migrator->generateChangeScript($schema);
+	}
+
 	/**
 	 * remove all tables defined in a database structure xml file
 	 *