DB-768 test case for 5.6 crash

mysql-test/suite/tokudb.bugs/r/db768.result

+set default_storage_engine='tokudb';
+drop table if exists t;
+create table t (id int primary key);
+set autocommit=OFF;
+lock tables t write;
+optimize table t;
+Table	Op	Msg_type	Msg_text
+test.t	optimize	status	OK
+unlock tables;
+drop table t;

mysql-test/suite/tokudb.bugs/t/db768.test

+# test case for DB-768
+source include/have_tokudb.inc;
+set default_storage_engine='tokudb';
+disable_warnings;
+drop table if exists t;
+enable_warnings;
+create table t (id int primary key);
+set autocommit=OFF;
+lock tables t write;
+optimize table t;
+unlock tables;
+drop table t;