[JENKINS-20074] When displaying an uncaught exception, if we are unable to write the content, just do nothing.
[FIXES JENKINS-19622] Replace hudson.model.Trigger#timer with jenkins.util.Timer, which exposes a ScheduledExecutorService. Up to 10 additional threads will be created to run pending tasks even if running tasks are blocked.

Also, move static initialization of timers to the classes which require them.
We must still initialize and clean up the legacy Trigger#timer
Naming convention
Synchronize access to the ScheduledExecutorService so that we can avoid NPE's during failed startup and lazily initialize it safely.
Null check
Remove meaningless initialization
Needs to build now with '-A'

This is presumably related to https://github.com/jenkinsci/jenkins/pull/956
but I don't fully understand what difference this makes.
[FIXED JENKINS-20191] Add Test button to check proxy connection
fixed typo
Use Common HttpClient instead of URLConnection
[JENKINS-15757] Ignore 'remember me' if disabled in configuration

The previous implementation of 'disable remember me' just removes the
checkbox from the UI. Users still can set the parameter using a web
browser extension, or patch the login page using a Greasemonkey script
and keep using the feature. And just after the feature is enabled, users
still might be able to use it if they loaded the login page early.

This change prevents that by checking the current configuration and, if
'remember me' is disabled, ignoring any headers set.
Better buttons into popups
Removed commented-out style
Fixed text alignment about icons on legend page
Merge pull request #997 from POPSuL/better-legend

Fixed text alignment about icons on legend page
[maven-release-plugin] prepare release jenkins-1.538
[maven-release-plugin] prepare for next development iteration
updated changelog for release
updated changelog as a part of the release