title: Warn about non-static ConfigurationClassPostProcessor declarations on @Configuration classes
body: <p>I use Spring 4.2.6.RELEASE. During initialization of my app I get such a warning:</p>
  
  <blockquote>
    <p>[WARN]
    org.springframework.context.annotation.ConfigurationClassPostProcessor
    enhanceConfigurationClasses: Cannot enhance @Configuration bean
    definition
    'org.springframework.security.oauth2.config.annotation.web.configuration.AuthorizationServerEndpointsConfiguration$TokenKeyEndpointRegistrar'
    since its singleton instance has been created too early. The typical
    cause is a non-static @Bean method with a
    BeanDefinitionRegistryPostProcessor return type: Consider declaring
    such methods as 'static'.</p>
  </blockquote>
  
  <p>I have found jira for a very similar problem:</p>
  
  <p><a href="https://jira.spring.io/browse/SPR-14234" rel="noreferrer">https://jira.spring.io/browse/SPR-14234</a></p>
  
  <p>but it is marked as closed and should be fixed in 4.2.6.RELEASE.</p>