Update whats new in Spring 3.2

Issue: SPR-10015
Update reference docs to a more modern CSS style

This change upgrade the framework to consume the newly-published
docbook-reference-plugin version 0.2.0, which includes among other
improvements a revamped CSS approach designed to look as similar
as possible to the way markdown files are rendered by GitHub.

See associated commit [1] at SpringSource's gradle-plugins repo for
further details.

Issue: SPR-10036

[1]: https://github.com/SpringSource/gradle-plugins/commit/b209c350ed76c10815815ab320c2379e8de3fec9
Introduce AnnotationAwareOrderComparator#INSTANCE

Prior to this change, the INSTANCE constant one could refer to on
AnnotationAwareOrderComparator actually referred to the constant
declared in the OrderAwareComparator superclass. Thus
AnnotationAwareOrderComparator#INSTANCE did not actually return an
AnnotationAwareOrderComparator but an OrderAwareComparator instead. This
commit introduces a dedicated constant on AnnotationAwareOrderComparator
to avoid this glitch.

Issue: SPR-10038
Merge pull request #188 from olivergierke/SPR-10038

# By Oliver Gierke
* SPR-10038:
  Introduce AnnotationAwareOrderComparator#INSTANCE
Polish whitespace and formatting
Add spring-test-mvc tests with Spring HATEOAS links

Issue: SPR-9886
Add MockMvcClientHttpRequestFactory

Issue: SPR-9917
Update maximum width of reference HTML

This change upgrade the framework to consume the newly-published
docbook-reference-plugin version 0.2.1 containing a maximum width
for the HTML reference guide.
Fix failing test from last commit

Issue: SPR-9917
Fix issue in Callable processing interceptor chain
Java 5 Closeable and Java 7 AutoCloseable automatically detected as destroy methods

Also, @Bean destroy method inference not applying for DisposableBean implementers anymore (avoiding double destruction).

Issue: SPR-10034
Final preparations for 3.2 RC2
Remove reflection usage in orm.hibernate4.*

Previously reflection was required when interacting with Hibernate 4 in
order to support both Hibernate 3 and Hibernate 4 since there were
non-passive changes in the APIs. Now that the Spring build uses Gradle
it is trivial to support multiple Hibernate versions.

This commit removes the reflection usage in orm.hibernate4.* by
creating a spring-orm-hibernate4 module that uses
gradle/merge-artifacts.gradle to build a single artifact but keep
distinct classpaths.

Issue: SPR-10039
Intermittent MBeanServerFactoryBeanTests failure

Prior to this commit the testWithLocateExistingAndExistingServer method
would fail if any preceding test called the ManagementFactory
getPlatformMBeanServer() method. In such situations the platform
server is located instead of the expected freshly created server.

These failures are more likely to happen when compiling with JDK 7
due to the fact that the reflection API no longer returns methods
in a consistent order.

Unfortunately there is no easy way to reset the platform MBean server
so the new code must resort to using reflection to access the private
static ManagementFactory.platformMBeanServer field.

Issue: SPR-9288
Remove unused imports
Merge pull request #179 from EzequielB/spring-aop-cleaning

* spring-aop-cleaning:
  Remove unused imports