refs #5510 get varchar expansion with prefix keys working in mysql 5.6.7

git-svn-id: file:///svn/mysql/tests/mysql-test@48517 c7de825b-a66e-492c-adef-691d508d4ae1

mysql-test/suite/tokudb.change_column/r/change_varchar_prefix_b.result

+DROP TABLE IF EXISTS t;
+SET SESSION TOKUDB_DISABLE_SLOW_ALTER=ON;
+SET SESSION DEFAULT_STORAGE_ENGINE='TokuDB';
+CREATE TABLE t (a VARCHAR(32), b VARCHAR(32), KEY(a(2)));
+SHOW CREATE TABLE t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `a` varchar(32) DEFAULT NULL,
+  `b` varchar(32) DEFAULT NULL,
+  KEY `a` (`a`(2))
+) ENGINE=TokuDB DEFAULT CHARSET=latin1
+ALTER TABLE t CHANGE COLUMN b b VARCHAR(100);
+ALTER TABLE t CHANGE COLUMN b b VARCHAR(256);
+DROP TABLE t;