* moved to jenkins.util.SystemProperties
* consistent naming getString/getInteger/getBoolean
* improved code formatting
Improved JavaDoc

Accomplished by centralizing calls to System.getProperty(String) and related into new file SystemProperties.java.
There, we first check for existence of system property; if not, we look for property in context.xml
This is done for "application" properties (like hudson.DNSMultiCast.disabled) but not for java properties (like user.name)

This should work across builds and even across jobs, and does not force us to load other builds.
(cherry picked from commit 2f59ffc4)

Conflicts:
	changelog.html

(cherry picked from commit b9d8f554)

This should work across builds and even across jobs, and does not force us to load other builds.

If we ever decide to develop a compatibility thunk library for these changes to help promote deployment in plugins,
then these classes being a nested type is problematic as they'll fail to load under onld Jenkins

prevent build index page to redirect anonymous user to login just because some artifact share fingerprints with another job

This is simpler: we do not need to inspect the configuration of the project.

Prevents multiple FingerprintActions.

[JENKINS-18224] Introduced Actionable.replaceAction, allowing getActions() to be deprecated except for subclasses.

FingerprintCleanupThread can now partially clean up a fingerprint record
by removing portions of it that's not referencing existing stuff.

[FIXED JENKINS-17125] FingerprintAction no longer need persist the build field thanks to new RunAction2.

[JENKINS-16845] Refinement to hotfix: if build field has already been cleared due to earlier warning, do not throw a new NPE.

Root cause seems to be broken serial form of FingerprintAction, probably caused by lazy loading.

Now that we're lazy loading builds, calling getBuildByNumber is not cheap.
So evaluate the 'ignore' flag before trying to load the build.

While several plugins implemented the interface under the old name, only core was checkcasting it.

build numbers might exhibit some uniformity that makes it problematic with %4==0, so switching to random.

The average memory saving should be about the same.

dependency graph. This functionality is enabled through a feature flag,
hudson.tasks.Fingerprinter.enableFingerprintsInDependencyGraph, which is off
by default.

- Rebuild the dependency graph as part of each fingerprint action.
  Fingerprinter.buildDependencyGraph adds information to the dependency graph
  for projects found in fingerprint records. Since the dependency graph is
  based on project, once a relationship is established between two projects,
  we can skip scanning subsequent builds of the projects. Entries in the
  graph added by the fingerprinter action will never automatically trigger
  downstream builds.

   core/src/main/java/hudson/tasks/Fingerprinter.java

- When reporting dependency changes, don't consider builds that no longer
  exist. This handles issues when projects are renamed, and new projects are
  created using the same name, causing the change to point to incorrect
  builds.

   core/src/main/java/hudson/model/AbstractBuild.java

- Tests.

   test/src/test/java/hudson/tasks/FingerprinterTest.java

Just import changes, from hudson.model.Jenkins -> jenkins.model.Jenkins,
and Javadoc comments.
Signed-off-by: NNigel Magnay <nigel.magnay@gmail.com>

Signed-off-by: NNigel Magnay <nigel.magnay@gmail.com>