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;