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

jenkins.model.Jenkins::getInstance() method is marked as @CheckForNull, but the most of Jenkins code does not actually check the return value. It leads to tons of static analysis errors, hence it is hard to analyze the code.

The change also adds annotations to old methods like Hudson::getInstance()
Signed-off-by: NOleg Nenashev <o.v.nenashev@gmail.com>

This matches fb65a2c3c8584a9ac4daa49ecbce7a540dc7f5a5 in remoting.

Even though SezpozModule.configure catches and ignores the faulty component, Guice still dies:
… hudson.ExtensionFinder$GuiceFinder <init>
SEVERE: Failed to create Guice container from all the plugins
com.google.inject.internal.guava.collect.$ComputationException: java.lang.NoClassDefFoundError: org/eclipse/jgit/storage/file/FileRepository
	at …
	at com.google.inject.Guice.createInjector(Guice.java:73)
	at hudson.ExtensionFinder$GuiceFinder.<init>(ExtensionFinder.java:279)

[FIXED JENKINS-25400] Rework fix of JENKINS-22769 (c04cdcd9) to put the burden on each listener to impersonate ACL.SYSTEM if it needs to.

Properly close listeners for asynchronous threads.
Signed-off-by: NOleg Nenashev <o.v.nenashev@gmail.com>

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

Resource leak may happen during the search of manifest file.
Signed-off-by: NOleg Nenashev <o.v.nenashev@gmail.com>

The issue is related to JENKINS-18351.
Signed-off-by: NOleg Nenashev <o.v.nenashev@gmail.com>

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

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