#463: Add ability for timeout to print full thread stack dump

Although originally this started based on #727: Fail on timeout displays stack of stuck thread …

This is a first naive attempt that (a) optionally adds information from ThreadMXBean#findMonitorDeadlockedThreads and (b) always adds full thread dump to exception message

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@dsaff and #727: Since the Timeout#createTimeoutException is now (?) in FailOnTimeout#createTimeoutException (statement) it would require to (1) subclass FailOnTimeout to override FailOnTimeout#createTimeoutException and (2) subclass Timeout to override Timeout#apply to create and return an instance of the new FailOnTimeout sublcass from before. I had hoped for more convenience...

Besides that I also stumbled over the fact that quite some interesting thread dump information (locks, monitors, synchronizers) can only be retrieved from ThreadMXBean from Java >= 1.6.

Thus, what do you think of the following naive and admittedly very ugly thoughts, when I want to have this extended thread dump?
* Is any poor mans plugin/extension attempt via an non-elegant reflection based class creation (e.g. there is a system property with the full qualified name of the dumping class) thinkable?
* Another ugly idea would be making JUnit a multi-project with an optional 1.6 compatible part, where this extended thread dump class can be placed. Of course this then could be packaged in whatever ugly style in a single JAR and again via system property + reflection plugged in... But this gets extremely dirty...