Do not prefetch async state if handler of the same type

This matches the behaviour of getInitialAsyncState (w/o prefetchAsyncState call)
and of getInitialState. If an async state depends on props, then one would need
to initiate its update directly from componentWillReceiveProps (like one would
do with regular state).

Author: andreypopp

lib/AsyncRouteRenderingMixin.js

@@ -13,7 +13,14 @@ var AsyncRouteRenderingMixin = {
   mixins: [RouteRenderingMixin],
 
   setRoutingState: function(state, cb) {
-    if (state.handler && isAsyncComponent(state.handler)) {
+    var currentHandler = this.state && this.state.handler;
+    var nextHandler = state && state.handler;
+
+    if (nextHandler &&
+        isAsyncComponent(nextHandler) &&
+        // if component's type is the same we would need to skip async state
+        // update
+        !(currentHandler && currentHandler.type === nextHandler.type)) {
       // store pending state and start fetching async state of a new handler
       this.setState(
         {pendingState: state},