If rbssh was invoked manually, DJANGO_SETTINGS_MODULE likely wouldn't be

set, and it would fail with an error. This could in theory also happen

if the environment isn't propagated from within Review Board down

through whatever process ended up invoking rbssh.
We now ensure we have this variable set, so that our code is guaranteed

to be able to access settings.

Ran rbssh localhost in a standard shell, and successfully logged into

a new SSH session. Previously, it would error out with a complaint about

settings.