Added 'Authentication service unavailable, please try again in a few minutes' Error

This is in regards to a pending pull request #27 ...

https://github.com/freeside/Freeside/pull/27

That pull request is about being *capable* of showing a message in the event the database was down. It currently displays 'no_preuser_setup'. 

This pull request is having the following error display instead of the default error mentioned above.

'Authentication service unavailable, please try again in a few minutes'

Feel free to let me know if you would prefer a different error, or if there are any questions or concerns.

Thanks!