Add validation on exists database before created

CodeIgniter don't content any methods of checking of database exists.
Please add validation on exists database before created to Forge Class by default:

protected $createDatabaseStr = 'CREATE DATABASE IF NOT EXISTS %s';

[lonnieezell]

You're right, it currently doesn't, and never has if memory serves correctly. I think this is a good addition, but not going to happen until after 4.0 final, since we've hit a feature freeze until release.