#403 - Use of EmailValidator for versions of PHP >= 5.3

See #403
I've not found a way to create a bridge class for using the EmailValidator in PHP 5.2 because of the namespaces. This fix allows for the use of the lib if you are using PHP 5.3 and leaves the usage of the previous validation otherwise.
As this PR will be merged in a new major version of Swiftmailer and because the `mime.grammar` is removed here, the Grammar class should be removed as well.