Add Index Downcases Table Name

This is a weird, and known issue with MySQL, using the `CREATE INDEX` syntax the table name is lowercased, e.g. `myTable` becomes `mytable`. That's what node-db-migrate [does right now][1]. Alternatively, it is suggested `ALTER TABLE myTable ADD INDEX myIndex (myColumn)`. If this is a desired fix I'm sure I could whip up a pull and test case.

[Read more about the bug][2] (currently marked "Verified")

[1]: https://github.com/kunklejr/node-db-migrate/blob/master/lib/driver/mysql.js#L172
[2]: http://bugs.mysql.com/bug.php?id=48875