create partitioned table with bigint column fail

[tiancaiamao]

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.

create table t1 (a bigint unsigned not null) partition by range(a) (
  partition p0 values less than (10),
  partition p1 values less than (100),
  partition p2 values less than (1000),
  partition p3 values less than (18446744073709551000),
  partition p4 values less than (18446744073709551614)
);
insert into t1 values (5),(15),(105),(1005);
insert into t1 values (18446744073709551000+1);
insert into t1 values (18446744073709551614-1);

2. What did you expect to see?

No error.

3. What did you see instead?

ERROR 1493 (HY000): VALUES LESS THAN value must be strictly increasing for each partition

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

master 09fb68a