Polish (major) MVC async processing interceptors

New afterTimeout and afterCompletion callbacks

afterTimeout can provide a concurrent result to be used instead of the
one that could not be set or returned on time

Interceptor exceptions cause async processing to resume treating the
exception as the concurrent result

Adapter classes for convenient implementation of the interfaces

Issue: SPR-9914
Polish (minor) RequestMappingHandlerAdapter

Revise order of fields reflecting configurable vs internal fields and
also grouping them accordingly.
Add config options for MVC async interceptors

The MVC namespace and the MVC Java config now allow configuring
CallableProcessingInterceptor and DeferredResultProcessingInterceptor
instances.

Issue: SPR-9914
Fix failing test
Delete unused imports
Configurable locales in MockHttpServletRequest

Prior to this commit the MockHttpServletRequest constructor chain set
the preferred local to Locale.ENGLISH. Furthermore, it was possible to
add additional preferred locales "in front" of ENGLISH; however, it was
not possible to delete ENGLISH from the list of preferred locales.

This commit documents the fact that ENGLISH is the default preferred
locale and makes it possible to set the list of preferred locales via a
new setPreferredLocales(List<Locale> locales) method.

Issue: SPR-9724
Update changelog

Issue: SPR-9724
Fix package cycles in spring-test

Code introduced in conjunction with SPR-5243 introduced package cycles
between the ~.test.context.web and ~.test.context.support packages. This
was caused by the fact that ServletTestExecutionListener extended
AbstractTestExecutionListener.

To address this, ServletTestExecutionListener now implements
TestExecutionListener directly.

Issue: SPR-9924
Update changelog

Issue: SPR-9593
Reduce code duplication in ContextLoaderUtils

Prior to this commit, the following two methods in ContextLoaderUtils
contained almost identical loops for traversing the test class
hierarchy:

 - resolveContextLoaderClass(Class<?>, String)
 - resolveContextConfigurationAttributes(Class<?>)

With this commit, resolveContextLoaderClass() no longer traverses the
class hierarchy. Instead, it now works directly with the resolved list
of ContextConfigurationAttributes, thereby removing code duplication.

Issue: SPR-9918
Fix package cycles in spring-test

Code introduced in conjunction with SPR-5243 introduced package cycles
between the ~.test.context and ~.test.context.web packages. This was
caused by the fact that ContextLoaderUtils worked directly with the
@WebAppConfiguration and WebMergedContextConfiguration types.

To address this, the following methods have been introduced in
ContextLoaderUtils. These methods use reflection to circumvent hard
dependencies on the @WebAppConfiguration and
WebMergedContextConfiguration types.

 - loadWebAppConfigurationClass()
 - buildWebMergedContextConfiguration()

Issue: SPR-9924
Polish whitespace
Allow 'arg-type' matches against element body

Allow the body of 'arg-type' XML elements to be used as an alternative to
'match' attribute when defining a 'replace-method' in XML configuration.

This change has been introduced primarily to support the samples printed
in the Apress 'Pro Spring' book.

Issue: SPR-9812
Merge pull request #153 from gid79/SPR-9812

* SPR-9812:
  Allow 'arg-type' matches against element body
  Polish whitespace