mysql supports unix socket

mysql now supports unix socket, postgresql already has as you can see here: http://www.postgresql.org/docs/8.3/static/libpq-connect.html

basic usage:
```
local db = require 'DBI'
local con, err = assert(db.Connect('MySQL', 'tupana', 'tupana', 'r4nd0m', '/tmp/mariadb.sock', nil))
```