RFR: Implement barriers to maintain connection matrix

[Roman Kennke]

.. as subject says.

The connection matrix is implemented in its own class.

The stuff is not optimized yet.

Christine's connection matrix code is still there, but no longer
operational.

-XX:+UseShenandoahMatrix turns on matrix bookkeeping.
-XX:+PrintShenandoahMatrix prints the matrix at end of marking.
-XX:+VerifyShenandoahMatrix verifies the matrix at end of marking.

For now, it needs -XX:ArrayCopyLoadStoreMaxElem=0 to turn of an
arraycopy optimization that requires additional barriers too.

It should not have measurable impact when not turned on.


Ok?

http://cr.openjdk.java.net/~rkennke/thematrix/webrev.00/

Roman