Improve error messaging when there is duplicate key or foreign key names

CREATE TABLE t111 (

  id int(11) NOT NULL PRIMARY KEY,

  a int(11) NOT NULL,

  b int(11) NOT NULL,

  c int not null,

  CONSTRAINT test FOREIGN KEY (b) REFERENCES t111 (id)

) ENGINE=InnoDB DEFAULT CHARSET=latin1;

CREATE TABLE t112 (

  id int(11) NOT NULL PRIMARY KEY,

  a int(11) NOT NULL,

  b int(11) NOT NULL,

  c int not null,

  CONSTRAINT test FOREIGN KEY (b) REFERENCES t61 (id)

) ENGINE=InnoDB DEFAULT CHARSET=latin1;

ERROR 1005 (HY000): Can't create table `test`.`t112` (errno: 121 "Duplicate key on write or update")

MariaDB [test]> show warnings;

+---------+------+----------------------------------------------------------------------------------+

| Level   | Code | Message                                                                          |

+---------+------+----------------------------------------------------------------------------------+

| Error   | 1005 | Can't create table `test`.`t112` (errno: 121 "Duplicate key on write or update") |

| Warning | 1022 | Can't write; duplicate key in table 't112'                                       |

+---------+------+----------------------------------------------------------------------------------+

2 rows in set (0.00 sec)