Support meta-annotation attr overrides in the TCF

Prior to this commit, the Spring TestContext Framework (TCF) supported
the use of test-related annotations as meta-annotations for composing
custom test stereotype annotations; however, attributes in custom
stereotypes could not be used to override meta-annotation attributes.

This commit addresses this by allowing attributes from the following
annotations (when used as meta-annotations) to be overridden in custom
stereotypes.

- @ContextConfiguration
- @ActiveProfiles
- @DirtiesContext
- @TransactionConfiguration
- @Timed
- @TestExecutionListeners

This support depends on functionality provided by
AnnotatedElementUtils. See the 'Notes' below for further details and
ramifications.

Notes:

- AnnotatedElementUtils does not support overrides for the 'value'
  attribute of an annotation. It is therefore not possible or not
  feasible to support meta-annotation attribute overrides for some
  test-related annotations.
- @ContextHierarchy, @WebAppConfiguration, @Rollback, @Repeat, and
  @ProfileValueSourceConfiguration define single 'value' attributes
  which cannot be overridden via Spring's meta-annotation attribute
  support.
- Although @IfProfileValue has 'values' and 'name' attributes, the
  typical usage scenario involves the 'value' attribute which is not
  supported for meta-annotation attribute overrides. Furthermore,
  'name' and 'values' are so generic that it is deemed unfeasible to
  provide meta-annotation attribute override support for these.
- @BeforeTransaction and @AfterTransaction do not define any attributes
  that can be overridden.
- Support for meta-annotation attribute overrides for @Transactional is
  provided indirectly via SpringTransactionAnnotationParser.

Implementation Details:

- MetaAnnotationUtils.AnnotationDescriptor now provides access to the
  AnnotationAttributes for the described annotation.
- MetaAnnotationUtils.AnnotationDescriptor now provides access to the
  root declaring class as well as the declaring class.
- ContextLoaderUtils now retrieves AnnotationAttributes from
  AnnotationDescriptor to look up annotation attributes for
  @ContextConfiguration and @ActiveProfiles.
- ContextConfigurationAttributes now provides a constructor to have its
  attributes sourced from an instance of AnnotationAttributes.
- ContextLoaderUtils.resolveContextHierarchyAttributes() now throws an
  IllegalStateException if no class in the class hierarchy declares
  @ContextHierarchy.
- TransactionalTestExecutionListener now uses AnnotatedElementUtils to
  look up annotation attributes for @TransactionConfiguration.
- Implemented missing unit tests for @Rollback resolution in
  TransactionalTestExecutionListener.
- SpringJUnit4ClassRunner now uses AnnotatedElementUtils to look up
  annotation attributes for @Timed.
- TestContextManager now retrieves AnnotationAttributes from
  AnnotationDescriptor to look up annotation attributes for
  @TestExecutionListeners.
- DirtiesContextTestExecutionListener now uses AnnotatedElementUtils to
  look up annotation attributes for @DirtiesContext.

Issue: SPR-11038
Merge pull request #421 from sbrannen/SPR-11038

* SPR-11038:
  Support meta-annotation attr overrides in the TCF
Fix various javadoc warnings
Fix synchronization issue in StompSubProtocolHandler

Two concurrent threads should not send a message on a single WebSocket
session at the same time, for example see:
http://docs.oracle.com/javaee/7/api/javax/websocket/RemoteEndpoint.Basic.html

In StompSubProtocolHandler it is quite possible that multiple messages
may be broadcast to a single WebSocket client concurrently.

This change adds synchronization around the sending of a message to a
specific cilent session.

Issue: SPR-11023
Add ability to customize message channels

@EnableWebSocketMessageBroker message channel configuration can now be
customized via WebSocketMessageBrokerConfigurer. It is necessary to
make this easy and even required as part of the basic configuration
since by default the message channels are backed by a thread pool of
size 1, not suitable for production use.

Issue: SPR-11023
General polish of new 4.0 classes

Apply consistent styling to new classes introduced in Spring 4.0.

- Javadoc line wrapping, whitespace and formatting
- General code whitespace
- Consistent Assert.notNull messages
Consistent whitespace after imports

Update code to have a consistent number of new-line characters after
import statements.
Detect cache hit with multiple @Cachables

Fix CacheAspectSupport to consider a cache hit from any of the multiple
@Cachables that may have been specified using the @Caching annotation.

Prior to this commit the following scenario would never produce a hit:

	@Caching(cacheable = {
		@Cacheable(value = "c1", unless = "#result.size() < 4"),
		@Cacheable(value = "c2", unless = "#result.size() > 3")
	})

Issue: SPR-11124
XML namespace for configuring WebSocket, STOMP.

This commit describes the XML syntax with a XSD file for the websocket namespace.
XML examples are used for our testsuite.

Issue: SPR-11063
Add <websocket:handler-mappings/> XML configuration support

Issue: SPR-11063