[JENKINS-20951] [JENKINS-18410] Did not make it into 1.544 due to validated merge holdups (mostly randomly failing tests, sigh).

[FIXED JENKINS-20951] XmlFile.read/unmarshal needs to catch general XStreamException so as to include CannotResolveClassException, thrown when a TopLevelItem provided by a plugin is unloadable.

[FIXED JENKINS-18410] AbstractTestResultAction should be a RunAction2 so it need not persist its owning build.

[FIXED JENKINS-17929] Pick up transport authentication from groovysh command, by overriding run rather than main.

Defer the notification to avoid deadlock.

The size is in wchar_t, not in bytes

Added a patched version of jzlib from
https://github.com/kohsuke/jzlib/tree/jzlib-1.1.3-kohsuke-1 to better
understand the deflate problem.

Implemented the hook

Integrated the fix in Stapler.

[JENKINS-19622] Merged #989: allow background tasks to run simultaneously, preventing task blockage.