Summary:
Ref T1536. None of this code is reachable.
Implements new-auth login (so you can actually login) and login validation (which checks that cookies were set correctly).
Test Plan: Manually enabled FB auth, went through the auth flow to login/logout. Manually hit most of the validation errors.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T1536
Differential Revision: https://secure.phabricator.com/D6162
