Clean up a live hack from wmf-deployment r53208: option to short-circuit math path and file existence checks.
Adds $wgMathCheckFiles setting:
/**
- Normally when generating math images, we double-check that the
- directories we want to write to exist, and that files that have
- been generated still exist when we need to bring them up again. *
- This lets us give useful error messages in case of permission
- problems, and automatically rebuild images that have been lost. *
- On a big site with heavy NFS traffic this can be slow and flaky,
- so sometimes we want to short-circuit it by setting this to false. */
$wgMathCheckFiles = true;