8144996: Replace the HeapRegionSetCount class with an uint
Reviewed-by: brutisso, jwilhelm

8145092: Use Unified Logging for the GC logging
Summary: JEP-271. VM changes contributed by brutisso, test changes contributed by david.
Reviewed-by: sjohanss, david, brutisso
Contributed-by: bengt.rutisson@oracle.com, david.lindholm@oralce.com

8137756: Remove hrs_err_msg and hrs_ext_msg from heapRegionSet
Reviewed-by: pliden, mgerdin

8079792: GC directory structure cleanup
Reviewed-by: brutisso, stefank, david