Make it easier to add new Message Converters to AnnotationMethodHandlerAdapter

See https://support.springsource.com/spring_support_client_getIncidentById/9995

I needed to use MarshallingHttpMessageConverter (so @RequestBody could bind a POST of XML to a POJO). AnnotationMethodHandlerAdapter is preconfigured in its constructor with several MessagConverters, but not MarshallingHttpMessageConverter. Using the <mvc:annotation-config/> tag, it was nearly impossible to add this MessageConverter to the AMHA. Per Spring Support, I had to write a BeanPostProcessor to look for the AMHA and then add the MTHC (and to add insult to injury, it was an array!).

There should be a simpler way to add MessageConverters; in fact, if they are found in the application context they should be added automatically, or they should be added via the mvc:annotation-config. Or anything more elegant than the BeanPostProcessor.

Also section 19.9 of the reference document implies that MarshallingHttpMessageConverter is configured by default, but it's not.