Remove Toran Proxy support

Summary: We're not using it, as it doesn't cache enough to improve our reliablity. Replaced with --cache-dir.

Reviewed By: @JoelMarcey

Differential Revision: D1561742
Make Framework::installDependencies() final, add <<Override>> where appropriate

Summary: The new hooks mean there's no need to override installDependencies(), and implementing the hook makes it clearer what's going on.

Add <<Override>> to isInstalled just for future safety.

Reviewed By: @JoelMarcey

Differential Revision: D1561812
Reserve / fix error codes.

Summary: Reserve error codes for an upcoming commit.

Also fix one instance of overlapping error codes.

Reviewed By: @elgenie

Differential Revision: D1563423
Tune pcre cache lookup

Summary: In the AHM for pcre cache, optimistically check for
StringData pointer equality before doing a full
comparison.

Reviewed By: @edwinsmith

Differential Revision: D1557919