Summary:
Ref T13098. Currently, it lives in `init-script.php`. Move it to a separate file for similarity with `support/PhabricatorStartup.php`.
Two small changes here:
- `dirname(dirname(...))` adjustments for new path.
- Remove `memory_limit(-1)`, this is adjusted by the libphutil init script already.
Test Plan: Ran `arc`.
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T13098
Differential Revision: https://secure.phabricator.com/D19687
