Made redirect URLs keep query params

This commit makes the redirect back to the client app maintain the query arguments that were passed with the original authorise. This is required for a number of apps including the Meteor accounts packages (http://github.com/uowits/meteor-accounts-uow).

The OAuth2 RFC says that OAuth2 providers MUST implement this functionality.
http://tools.ietf.org/html/rfc6749#section-3.1.2

> The redirection endpoint URI MUST be an absolute URI as defined by
> [RFC3986] Section 4.3.  The endpoint URI MAY include an
> "application/x-www-form-urlencoded" formatted (per Appendix B) query
> component ([RFC3986] Section 3.4), which MUST be retained when adding
> additional query parameters.  The endpoint URI MUST NOT include a
> fragment component.