plugin might erranously put null into the collection, so filter them out

Apache in its default configuration botches this: http://stackoverflow.com/a/9933890/12916

Conflicts:
	core/src/main/java/hudson/Functions.java
	core/src/main/java/hudson/markup/MyspacePolicy.java
	core/src/main/java/hudson/util/RobustReflectionConverter.java
	core/src/main/resources/lib/layout/layout.jelly
	war/pom.xml

This reverts commit 2d40b7e7.

This reverts commit b32d0e4f.

This reverts commit 6a31d6eb.

This reverts commit 037393c2.

When printing AbstractBuild.BuildingRemotely message to log, also indicate any (non-self) labels of the node.
This is invaluable when diagnosing problems with a build on a cloud slave after the slave has been deprovisioned.
If the node name by itself does not indicate what type of machine it was, you would have a hard time guessing.

[FIXED SECURITY-109] SECURITY-55 fix to BuildTrigger configuration failed if downstream project was not visible.

[FIXED SECURITY-107] When security-related fields in Jenkins cannot be unmarshaled, it is best to halt startup.

[FIXED SECURITY-93] PasswordParameterDefinition should serve existing default value in encrypted form.
And strengthen functional tests (using configRoundTrip) to ensure that the same mistake is not made elsewhere.