Add missing User-Interactive fields. Only add access_token if one was given.

client.go

@@ -75,7 +75,9 @@ func (cli *Client) BuildBaseURL(urlPath ...string) string {
 	parts = append(parts, urlPath...)
 	hsURL.Path = path.Join(parts...)
 	query := hsURL.Query()
+	if cli.AccessToken != "" {
 		query.Set("access_token", cli.AccessToken)
+	}
 	hsURL.RawQuery = query.Encode()
 	return hsURL.String()
 }

responses.go

@@ -42,6 +42,9 @@ type RespUserInteractive struct {
 	} `json:"flows"`
 	Params    map[string]interface{} `json:"params"`
 	Session   string                 `json:"string"`
+	Completed []string               `json:"completed"`
+	ErrCode   string                 `json:"errcode"`
+	Error     string                 `json:"error"`
 }
 
 // RespRegister is the JSON response for http://matrix.org/docs/spec/client_server/r0.2.0.html#post-matrix-client-r0-register