R1:727bc2234c3a

Capitalize "OPcache" more consistently

Summary: Fixes T13174. PHP spells this "OPcache" (lowercase "c"); we're inconsistent. Be more consistent.

Test Plan:
- `git grep OPCache`
- `git grep -i opcache | grep -v opcache | grep -v OPcache`

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13174

Differential Revision: https://secure.phabricator.com/D19538