fix specifying multiple auth servers; auth refactor
bump go-nsq
sync with new go-nsq changes
Merge pull request #370 from jehiah/lookup_authd_filter_370

lookupd: support filtering response based on auth state
util: make some HTTP response code reusable
nsqlookupd: provide versioned unwrapped response formats and consistent endpoint names
nsqd: refactor HTTP response formatting
nsqlookupd: update HTTP tests
util: more correct content type; add custom content type as return indicator
util: return empty response instead of 'null'
util: add APIRequestNegotiateV1
util/lookupd: add GetVersion helper
util/lookupd: use net.JoinHostPort for correctness
nsqadmin: unexport graphiteGet
util/lookupd: negotiate V1 response
nsqd: add suite of HTTP tests; update others to negotiate
nsqadmin: add helpers to query backwards compatible nsqd
nsqadmin: forwards/backwards compatible nsqd/nsqlookupd HTTP requests