Added option to passthru request data on auth.

This relates to Hawk pull request #121 ( https://github.com/hueniverse/hawk/pull/121 )

We needed a way to pass the full request object through to our authentication functions. This will check if a passthru option is set to true and, if it is, add the full request data to to settings.hawk object. This is similar to the passReqToCallback option in Passport.