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