Following the changes made in ff99bb07, Tomcat’s WebAppClassLoader is
set as the thread context class loader of the main thread. If Tomcat
was stopped while the main thread was still running (typically as a 
result of a startup failure), this had the unwanted side-effect of
causing Tomcat to report that the application had started a thread named
main and had failed to stop it.

This commit updates TomcatEmbeddedServletContainer so that, during stop
processing, the current thread’s context class loader is reset before
Tomcat is stopped. This prevents Tomcat from incorrectly believe that
the application has started and failed to stop the main thread.

Closes gh-5357

Closes gh-5335

See gh-5335

Prevent the validation support to kick in if the Validation API is not
available.

Closes gh-5353

Support for Velocity has been deprecated in Spring Framework 4.3 with
the plan being to remove it in 5.0. This commit deprecates Spring
Boot's support in 1.4, with the plan being to remove it in 2.0.

Closes gh-5276

Previously, if Couchbase was available on the classpath but not
configured, Spring Boot would attempt to scan the project for
repositories anyway.

This commit makes sure that it only happens if an infrastructure
bean required is present. The tests have also been rewritten to better
reflect what would happen in practice.

Closes gh-5349

In certain environments, such as Jetty configured with centralized
logging, Spring Boot's logging system can be problematic.

This commit adds support for using the existing LoggingSystem system
property, configured with a value of none, to disable the logging
system and rely on the standard logging configuration mechanism for
whatever logging framework is in use.

Closes gh-3571

* gh-5310:
  Upgrade to Gson 2.6.2

Closes gh-5310

* pr/5345:
  Polish

Closes gh-5345

Previously, the ehcache statistics were computed on the activity of the
last minute which gives a "live" overview. All others cache managers,
including JCache, provides a "cumulative" metrics (i.e. the hit/miss
ratio since the creation of the cache or the last time it got cleared).

Ths commit aligns the ehcache statistics to provide a similar semantics
as the other cache managers. The side effect is that the metrics are now
available, even if there is no cache activity at all at the moment.

Closes gh-4891

Assert using epoch time

Add TimeZone in date assertion

This commit updates `GitInfo` to use a proper `java.util.Date` rather
than a raw String. Because the Maven and Gradle plugin do not agree on a
format, `ProjectInfoAutoConfiguration` now registers a `Converter` that
is taking care of translating the raw `String` to a `Date`.

See gh-2484

This commit updates "simple" configuration classes to use constructor
injection. Simple means that there are no optional dependencies
(@Autowired(required=false) is not used), and none of the dependencies
use generics.

Configuration classes that are not simple will be updated in a second
pass once https://jira.spring.io/browse/SPR-14015 has been fixed.

See gh-5306

* pr/5328:
  Polish contribution
  Rename HealthIndicatorAutoConfigurationProperties

Closes gh-5328

Closes gh-5326

* pr/5303:
  Polish contribution
  Add Cache Properties for RabbitMQ

Closes gh-5303

Closes gh-3502

* pr/3492:
  Polish contribution
  rebase to master
  Info endpoint

`InfoProvider` is now `InfoContributor` and contributes to the `Info`
instance via a builder. The `Info` instance is immutable. Each
contributor can be disabled via the `management.info.<name>.enabled`
key or all can be disabled using `management.info.defaults.enabled` (this
is similar to what the health endpoint does).

By default, all keys from the environment starting with `info.` are
exposed. If a `git.properties` file is present in the classpath, the
content of `GitInfo` is exposed using the `git` key.

A `SimpleInfoContributor` and `AbstractEnvironmentInfoContributor` are
available for convenience. `InfoContributor` instances can be ordered
the usual way, with a default order provided by
`InfoProviderAutoConfiguration#DEFAULT_ORDER`.

Closes gh-3492

See gh-3492

This commit moves `GitInfo` to a general "project info" area that will be
further improved with others project related information.

Deprecate `spring.git.properties` in favour of `spring.info.git.location`

Closes gh-2484

* pr/5318:
  Polish

Closes gh-5318

Closes gh-4283

Previously, only dependency management for logback-classic was
provided. This meant that it was possible for logback-core, upon
which logback-classic depends, to have a different version.

This commit adds dependency management for logback-core, thereby
ensuring that the two dependencies will have the same version.

Closes gh-5304

Shutdown handling has been improved so that it will run after any
EntityManagerFactory beans have been closed. This ensures that Hibernate
can, if configured to do so, drop its schema during restart processing.
Without this change, a benign exception could be logged if the database
was shutdown before Hibernate.

Closes gh-5305