Update license and copyright in all files

https://gist.github.com/henriquemoody/69d1399ba83d389e0974

The code in the gist above, written in PHP, was used to make most of these changes. It is not 100% reliable, that's why every file must be checked.

Fix #1557
Surely `This file is part of PHPUnit.` rather than `This file is part of the PHPUnit.`?