Previously, the launch script used which to determine the availability
of start-stop-daemon. which isn’t available by default on all OSs.
For example, it’s not available by default on CentOS 5.

This commit updates the launch script to use type when determining if
start-stop-daemon is available. This improves the portability of the
script and makes the use of type consistent throughout the script.

Closes gh-4925

Previously, the launch script would wait for the pid file to exist
before continuing. This didn’t work 100% of the time as it left a 
window where the file had been created but the PID had not been written
to it that could result in an incorrect report of the app failing to
start.

This commit updates the script to wait for the file to have a size
greater than zero before continuing. This ensures that the pid has
been written to the file before the pid is read from the file and used
to check that the process is running.

Closes gh-4923

Closes gh-4932

Update SpringApplication to publish an ExitCodeEvent when a valid exit
code is known.

Fixes gh-4804

Update exit code support to allow the ExitCodeGenerator interface to
be placed on an Exception. Any uncaught exception implementing the
interface and returning a non `0` status will now trigger a System.exit
with the code.

Fixes gh-4803

Closes gh-4821

* pr/4831:
  Fixed the check whether Log4j2 is available on the classpath

In Spring Boot 1.3.1 the class 'org.apache.logging.log4j.LogManager'
is used to check which logging backend is in use. But this class is
part of the log4j-api.jar and not part of the log4j-core.jar.
That means the check is invalid, as it does not detect the actual
core implementation of Log4j2 correctly.

When you want to redirect Log4j2 logging via SLF4J, a NPE occurs
each time the application is reloaded by the devtools, because the
class Log4j2RestartListener tries to shutdown Log4j2 resources.
This is done by accessing some internal shutdown method via
reflection. The method that is being looked for does not exist
when the log4j-api.jar is available only on the classpath,
resulting in a NPE. This causes the application to stop,
disappearing from the Spring Boot Dashboard in Eclipse

Closes gh-4831

Closes gh-4847

Issue #4533 was supposed to make BasicBatchConfigurer public again but
unfortunately only the class visibility was changed. This commit makes
sure it can be overridden.

Closes gh-4888

Update the Oomph instructions.

Closes gh-4844

* pr/4867:
  Fix invalid port number in doc

Closes gh-4867

By type is too restrictive and surprising for users who wanted to add their
own MetricReaderPublicMetrics for other reasons.

Closes gh-4839

# Conflicts:
#	spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/websocket/WebSocketAutoConfiguration.java

Tomcat's websocket support requires Java7 or later. That commit makes
sure to register its support only when such requirement is met.

Closes gh-4846

Clarify that "spring.config.*" properties doesn't work in configuration
files.

Closes gh-4838

* pr/4829:
  Change redirect in initscript to support old bash

`&>>` syntax is bash version 4. This fix allows to support older
versions.

Fixes gh-4820
Closes gh-4829

* pr/4837:
  Polish test

Closes gh-4837

See gh-4809

See gh-4789

when the logname is empty it replaces it with the root logger name.

Fixes gh-4808

* pr/4806:
  Fix typos

Closes gh-4806

Closes gh-4786