Move open_basedir and safe_mode checks into new setup

Summary: Newer and shinier!

Test Plan: Intentionally misconfigured myself into all three setup failures (safe_mode, open_basedir/fatal, open_basedir/nonfatal).

Reviewers: chad, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2228

Differential Revision: https://secure.phabricator.com/D4589