Psr0Fixer to tokens

I've rewritten the Psr0Fixer to use tokens instead of raw string, and I've added a leading `<?php` to all test-cases to make `token_get_all` work.

There's one test that fails though: the leading namespace test. Is it truly required behaviour for the fixer to remove leading whitespace? (it isn't mentioned in the PSR-0 standard)

This PR implements the last TODO in #489.
When you have many (real many!) namespaces in one class then you may not change last of them.
Why? You change collection size during iteration. When inserting at index 4 you silently move token that was on index 40 to 41. And you use indexes here to determine flow.
Please use backward for iteration instead of foreach loop.