Update ChoiceParameterDefinition

The "it.value" don't exist, so we need to set the defaultParameterValue. 

It help me display correctly parameter for my multilauncher plugin. 
Note that other ParameterDefinition use the default value to display parameter, so IMO it is safe to do this.

Better debug messages in JSONSignatureValidator

AtomicFileWriter.commit should use Util.deleteFile so as to get a more meaningful error message in case the deletion fails.
The following is not helpful in terms of diagnosing the root problem:
java.io.IOException: Unable to delete /…/jobs/demo/builds/…/workflow/3.xml
	at hudson.util.AtomicFileWriter.commit(AtomicFileWriter.java:112)
	at hudson.XmlFile.write(XmlFile.java:179)
	at org.jenkinsci.plugins.workflow.support.storage.SimpleXStreamFlowNodeStorage.saveActions(SimpleXStreamFlowNodeStorage.java:106)
	at …

The use case that led me here was to use this from workflow which relies primarily on Java serialization

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>

[FIXED JENKINS-22514] In ZIP archives file separator must be '/'

Aggregate multiple FormValidations into one

Expose AbstractProject.AbstractProjectDescriptor#validateLabelExpression for plugins

IIUC, the issue here is that the request in question contains both a
valid session cookie AND basic authentication header, and that path
results in a failure because BasicHeaderProcessor expects one of
BasicHeaderAuthenticators to validate the basic authentication header
(without knowing that there's already a valid Authentication object that
came from the HTTP session, yet no BasicHeaderAuthenticator actually
processes this because BasicHeaderRealPasswordAuthenticator backs away
from doing that.

I think the corect fix is for BasicHeaderRealPasswordAuthenticator to
get rid of authenticationIsRequired check. This check instead belongs to
BasicHeaderProcessor, where it should be used to check if any
BasicHeaderAuthenticator should be consulted or not.

The problem with having this logic in
BasicHeaderRealPasswordAuthenticator is that this is just an
implementation of an extension point, and thus it needs to be removable.
As it stands right now in this fix, if this impl is removed,
JENKINS-25144 will be back again.

return authentication object instead of null if authentication is not
required - otherwise valid login fails with basic authentication