SI-7442 Update bundled Fork/Join pool (JSR166y)

- Updates ForkJoinPool and dependent classes to the latest jsr166y revisions:

    ForkJoinPool.java:
    Revision 1.185
    Sat Feb 16 20:50:29 2013 UTC (2 months, 2 weeks ago) by jsr166

    ForkJoinTask.java:
    Revision 1.100
    Tue Feb 5 17:09:54 2013 UTC (3 months ago) by jsr166

    ForkJoinWorkerThread.java:
    Revision 1.73
    Wed Nov 21 19:54:39 2012 UTC (5 months, 2 weeks ago) by dl

- Includes Akka-contributed `sun.misc.Unsafe` detection to support Android.
  See changeset 06d685c1bbd8a0d058ee8a3f374569f8097f2acc

- Adds private `CountedCompleter` class.
  This class is only visible and used in `ForkJoinPool.java`.

- Updates desired.sha1 for updated forkjoin.jar

- Resolves binary compatibility issues by
  (a) keeping package-private methods that are no longer used
  (b) adding dummy implementation of package-private method
      void registerWorker(WorkQueue w)