Part of twisted.spread.pb.PBClientFactory View Source
Login and get perspective from remote PB server.
Currently the following credentials are supported:
   L{twisted.cred.credentials.IUsernamePassword}
   L{twisted.cred.credentials.IAnonymous}
| Returns | A Deferred 
which will be called back with a RemoteReference
for the avatar logged in to, or which will errback if login fails. (type: Deferred) | |