[RootView] Asynchronously load the bundle to give time to configure t…

…he root view

If you construct an RCTRootView you may want to configure the executor. However the constructor synchronously calls `loadBundle` and sets up the executor and bridge. This is a quick fix that uses dispatch_async to allow the current pass of the runloop time to set up the executor.

Fixes facebook#288

React/Base/RCTRootView.m

@@ -318,7 +318,9 @@ - (void)setScriptURL:(NSURL *)scriptURL
   }
 
   _scriptURL = scriptURL;
-  [self loadBundle];
+  dispatch_async(dispatch_get_main_queue(), ^{
+    [self loadBundle];
+  });
 }
 
 - (void)layoutSubviews