R1:9f9716f81fce

Fix Firefox upload fatal

Summary:
Several problems:

- With fpm-warmup, 'PhabricatorAccessLog' is always loaded, even if it hasn't actually initialized. Use a global instead (barf). I'll fix this when I refactor index.php, hopefully soon.
- The 'POST' check isn't sufficient in Firefox for HTML5 uploads -- not 100% sure why, maybe it encodes post bodies differently? I added an additional '__file__' requirement, and will add this param to GET on all file uploads in a future diff.

See discussion in…