@EnableMBeanExport supports placeholders for its attributes now

Issue: SPR-11105
Optimized ImportAware processing to avoid re-reading class files
Properly handle InvocationTargetException in reflective JtaPlatform implementation
Polishing
Re-enabled tests for meta-annotations on interfaces

Issue: SPR-11108
Consolidate websocket/messaging code

Before this change spring-messaging contained a few WebSocket-related
classes including WebSocket sub-protocol support for STOMP as well
as @EnableWebSocketMessageBroker and related configuration classes.

After this change those classes are located in the spring-websocket
module under org.springframework.web.socket.messaging.

This means the following classes in application configuration must
have their packages updated:

org.springframework.web.socket.messaging.config.EnableWebSocketMessageBroker
org.springframework.web.socket.messaging.config.StompEndpointRegistry
org.springframework.web.socket.messaging.config.WebSocketMessageBrokerConfigurer

MessageBrokerConfigurer has been renamed to MessageBrokerRegistry and
is also located in the above package.
Fix remaining compiler warnings

Fix remaining Java compiler warnings, mainly around missing
generics or deprecated code.

Also add the `-Werror` compiler option to ensure that any future
warnings will fail the build.

Issue: SPR-11064
Add SubProtocolCapable interface

The addition of SubProtocolCapable simplifies configuration since it is
no longer necessary to explicitly configure DefaultHandshakeHandler
with a list of supported sub-protocols. We will not also check if the
WebSocketHandler to use for the WebSocket request is an instance of
SubProtocolCapable and obtain the list of sub-protocols that way. The
provided SubProtocolWebSocketHandler does implement this interface.

Issue: SPR-11111
Fix various typos

Fix a variety of typos throughout the project, primarily in
comments (javadoc or otherwise) but also in a handful of log messages
and a couple exception messages.

ISSUE: SPR-11123
Merge pull request #418 from ericdahl/doc-typos

* doc-typos:
  Fix various typos
Re-introduced custom StaxSource and StaxResult for Spring Web Services
Adapted getXmlAsSource implementation to avoid compilation failure in IntelliJ IDEA
Provide meta-annotation support for @Rollback

@Rollback now supports ANNOTATION_TYPE as a target, allowing it to be
used as meta-annotation.

Note: this change was accidentally omitted from the original commit for
SPR-7827.

Issue: SPR-7827