Support for users in views integration

The module Fivestar Extra allows rating of users.

I have received a few requests to add Views support, but I realise that all it needs is for VotingAPI to allow relationships with users.

I realise I could implement this with the "votingapi_relationships" hook, but as users are one of the base view types, I thought this very simple patch to VoingAPI itself might be appropriate.

Thank you!