DATAREST-106 - Spring 4.0 compatibility in ResourceProcessorInvokingHandlerAdapter.

Fix ResourceProcessorInvokingHandlerAdapter to call
getReturnValueHandlers() via reflection and deal with different
response types.

This change is necessary due to SPR-10519 which changed the API of
RequestMappingHandlerAdapter.getReturnValueHandlers() to return a
List rather than a HandlerMethodReturnValueHandlerComposite.

Original pull request: #114.