Change license from GPL v3 to MIT

[k00ni]

To make things real, finally. :)

According discussion in issue #90 (including permissions of relevant persons).

[white-gecko]

As I understand the MIT license, each file has to carry the license notice.

[k00ni]

Is outlining the license as in the following OK?

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

Source

[k00ni]

@white-gecko, I assume, you have nothing against the following header example of symfony? If so, then i would add it to all files soon.