Improve file mode.

- Remove tmp file on failed rename (prevent filling disk with tmp files)
- Support force revalidation via filesystem flag to prevent stampeding the cache
- Revert back to include method rather than serialize/deserialize to
  take advantage of opcode caches.
Improve APC mode.

- Check that APC is actually enabled.
- Do not store apc cache for cli mode.
- Make useAPC static property public to allow it to be explicitly
  enabled or disabled.
Merge branch 'apc-check'