Moves a MySQL-specific method to the MySQL adapter from the PDO adapter

It's a MySQL specific method, with a MySQL specific query, marked  with an `@TODO` to move it to the MySQL adapter. MySQLMySQLMySQL.

The method's not mentioned anywhere else in the code-base, but it's a public method, so who knows how it's being used. Removing it might break someone's use, but I can't see how moving it to the MYSQL adapter would: `PDOAdapter` is abstract, and the method call wouldn't have worked on anything but `MysqlAdapter`, so it seems like a safe bet.

Or go newkular, and just remove it. Or implement an equivalent for the other languages (`\d+`, something to do with the [sqlite_master](http://www.sqlite.org/faq.html#q7) table), but that's a PR for someone else.