so don't preprend ${rootURL} .. thx alexlehm

Tsk Tsk! Kohsuke you missed a possible NPE for people running hpi:run on plugins in fixing [JENKINS-6545]

I wasn't initially planning to do this, but it turns out more people needed this feature than I thought.

I left the text as is, but defined a mechanism to override this in the plugin, in a possibly context sensitive way. For example, a plugin can replace this text on a job-by-job basis, or by looking at some property/builder/etc.

pushed the winstone dependency to the <dependencies> so that we can see the source code during debugging

the UI.

Also, for the core build, require that all the dependency licenses are
available.

Use LinkedBlockingQueue to support unbounded requests. Previously this was limited to the max thread pool size (of ten).

- support invisible JobProperty