Fix issue with @RequestBody args that are type vars

The change to support generic @RequestBody arguments introduced in
3.2 M2 also introduced a regression in reading arguments that are
type variables. This change fixes the issue.

Issue: SPR-9964
Support Gradle/maven with multi version artifacts

Previously the publish-maven.gradle only supported having a single
artifact be marked as optional or provided. This causes problems now
that we are building modules that support multiple versions of an
artifact. For example, we compile against two versions of Tiles
artifacts with identical names, both of which need to be marked
optional.

This updates publish-maven.gradle to find all the artifacts and mark
them as optional as apposed to the first entry.
Merge pull request #185 from rwinch/maven-multi-version-artifact

* rwinch-maven-multi-version-artifact:
  Support Gradle/maven with multi version artifacts
Refactor Gradle script naming and organization

 - inline test-mvc and tiles3 .gradle files for clarity
 - rename merge-dist.gradle to merge-artifacts.gradle
 - polish Javadoc for merge-artifacts.gradle
 - move merge-artifacts.gradle into gradle subdirectory
 - move publish-maven.gradle into gradle subdirectory
Introduce jdiff Gradle task

The new jdiff task generates a report of API differences between the
current version (i.e. the value of `version` in gradle.properties) and
any older version of the framework, as specified by -DOLD_VERSION at
the command line, or defaulting to `previousVersion` in
gradle.properties.

Running the command requires a separate clone directory pinned to the
desired old version, as specified by -DOLD_VERSION_ROOT at the command
line. This creates challenges from a build automation perspective,
largely because Gradle doesn't (yet) have APIs for working with Git.

This task may be further automated and included in nightly CI runs, but
in the meantime, a number of reports back to 3.1.3.RELEASE have been
generated manually and uploaded to [1], where one can now find the
following entries in the directory listing:

 - 3.1.3.RELEASE_to_3.2.0.RC1
 - 3.2.0.M1_to_3.2.0.M2
 - 3.2.0.M2_to_3.2.0.RC1
 - 3.2.0.RC1_to_3.2.0.BUILD-SNAPSHOT

Ideally, the final entry there would be kept up-to-date on a daily
basis - again we may revisit doing so in the future. Going forward,
reports will be generated and uploaded manually on an as needed basis
and as part of the release process.

The goal of these reports are as follows:

 - to ease the process of ensuring backward compatibility

 - to aid in code reviews, particularly when reviewing large pull
   requests

 - to ease the process of creating migration guides for project
   maintainers, i.e. to help us remember what's changed

 - to allow ambitious end-users to discover what's been changing at the
   API level without without needing to wait for detailed "what's new in
   version X" and/or migration guide documentation

See documentation in jdiff.gradle for usage details.

Note that the jdiff-1.1.1 distribution as downloaded from [2] has been
added wholesale to the source tree under gradle/jdiff instead of
uploading JDiff jars to repo.springsource.org as we would normally do.
This is due to some unfortunate limitations in the implementation of the
jdiff ant task that require a phisical JDIFF_HOME directory. Checking in
the jars and various resources represents the simplest and most
pragmatic solution to this problem, though ambitious contributors are
free to do what's necessary to arrive at a more elegant arrangement.

[1]: http://static.springframework.org/spring-framework/docs
[2]: http://sourceforge.net/projects/javadiff/files/latest/download

Issue: SPR-9957
Set response to 503 for async requests that time out

Issue: SPR-10002