[GH-422] DDC-1574 - "new" operator

This issue is created automatically through a Github pull request on behalf of FabioBatSilva:

Url: https://github.com/doctrine/doctrine2/pull/422

Message:

http://www.doctrine-project.org/jira/browse/DDC-1574

Hi guys.

This path adds support for "new" operator

Usage :
```SQL
SELECT
new CustomerDTO(c.name, e.email, a.city)
FROM
Customer c
JOIN
u.email e
JOIN
u.address a
ORDER BY
u.name
```

Any simple class with a constructor could be used
but for the first version just scalar values are allowed.

it's a big patch, so any sugestion are welcome.

Thanks.