Take care about mariadb platform

Hi,
After upgrading to DBAL 2.5, I got an issue where I could not rename index while migrating because of MariaDB [versioning](http://en.wikipedia.org/wiki/MariaDB#Versioning) which outputs ```10.0.15-MariaDB-1~wheezy ``` as server version.

Because 10.x > 5.7 it loads new features from mysql 5.7 which are not available in mariadb ..