title: Spring Async issue when upgrading from 4.2.0.RC3 to 4.2.0.RELEASE
body: <p>I've a web application using the spring(4.2.x) artifacts spring-webmvc, spring-messaging, spring-websocket</p>
  
  <p>I've the below @Enable* annotations in my spring config java class</p>
  
  <pre><code>@EnableWebMvc
  @EnableWebSocketMessageBroker
  @EnableAsync
  @EnableMBeanExport
  </code></pre>
  
  <p>WebSocket is used for broadcasting messages to browser clients.
  And there are few async methods annotated with @Async</p>
  
  <p>The application was working fine with spring version 4.2.0.RC3. But when I changed it to the GA release 4.2.0.RELEASE, I get the below exception on startup. If I remove @EnableAsync it works fine, but I need the async functionality.</p>
  
  <pre><code>org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [org.springframework.core.task.TaskExecutor] is defined: expected single matching bean but found 4: clientOutboundChannelExecutor,messageBrokerTaskScheduler,clientInboundChannelExecutor,brokerChannelExecutor
      org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:366)
      org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:332)
      org.springframework.scheduling.annotation.AsyncAnnotationBeanPostProcessor.setBeanFactory(AsyncAnnotationBeanPostProcessor.java:128)
      org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeAwareMethods(AbstractAutowireCapableBeanFactory.java:1597)
      org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1565)
      org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:545)
      org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
      org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:305)
      org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
      org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:301)
      org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:201)
      org.springframework.context.support.PostProcessorRegistrationDelegate.registerBeanPostProcessors(PostProcessorRegistrationDelegate.java:228)
      org.springframework.context.support.AbstractApplicationContext.registerBeanPostProcessors(AbstractApplicationContext.java:682)
      org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:522)
      org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:667)
      org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:539)
      org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:493)
      org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
  </code></pre>