update watch index on error 401

Make progress anyway when the history is gone.

node/node.go

@@ -201,6 +201,15 @@ func (w *ConfigSyncer) Start() {
 			} else if err != nil {
 				// Log the error and start over.
 				log.Printf("Watch(): %s", err)
+
+				// If the error is code 401 ("index
+				// out of date"), start from the
+				// current index. TODO: consider
+				// calling loadFullConfig, or we might
+				// potentially lose some updates?
+				if etcdErr, ok := err.(*etcd.EtcdError); ok && etcdErr.ErrorCode == 401 {
+					w.setIndex(etcdErr.Index)
+				}
 			}
 		}
 	}()