Fixing an issue reported on StackOverflow

On StackOverflow someone was using the BankAccountCompositeTest as an example for composite DB testing but stumbled time after time against the error `PHPUnit_Extensions_Database_DB_DefaultConnection not found`.

A simple check of the filesystem would have made it clear that the class name is different, it wouldn't hurt to update the documentation and examples so people get a smooth experience testing databases.

The StackOverflow report can be found here: http://stackoverflow.com/questions/20280621/how-to-test-with-dbunit-using-composite/