Remove sessions helper spec.

Pending tests in the rspec run annoy me.
Login / logout links on main template.

Added message to index template to manually test login/logout.  Need
to come up with an automated way of testing this.
Session controller tests.

Automated tests for login/logout.  Apparently controller tests have
access to the session, even if integration tests do not.
User controller specs.

All of this is tested incidentally via the integration tests, but for
the sake of completion, test the user controller directly.