Permit RunnerStack.peek to return null in case it is not in use (for example, from a workflow), so that we do not get an NPE when trying to run a task that asks for checkpoints.
https://trello.com/c/DoCMV6gB/31-runnerstack

Conflicts:
	core/src/main/java/hudson/tools/InstallerTranslator.java

[FIXED JENKINS-20663] For now, go back to using ZipOutputStream from Ant that supports setting the filename encoding (present in java.util.zip only in Java 7+).

Set "X-UA-Compatible" meta tag (MSIE browsers only - forces browser compatibility mode)
JS based warning if Document Mode doesn't match IE version (MSIE browsers only)

All other places use this class for a td with help icon.
This improves rendering of the different strategies under "Restrict
project naming"

[JENKINS-2673] Clarify that suggestion means polling just once per hour

Correcting change made in #1176, which introduced an NPE, to restore original logic merely wrapped in a synchronized block.
Reproduced NPE in new functional test (original bug probably very hard to reproduce).

[JENKINS-14749] Suppress warnings about expected exception from prototype.js#HAS_EXTENDED_CREATE_ELEMENT_SYNTAX.

[JENKINS-14749] Temporarily work around CSS errors by just suppressing the warnings until they can be fixed.

The JNLP port is not interesting enough to warrant logging at INFO during every startup, including the vast majority of functional tests which do not even use JNLP slaves.

updated German translation