Request for review - 8013184 CMS: Call reset_after_compaction() only if a compaction has been done

[Jon Masamitsu]

8013184: CMS: Call reset_after_compaction() only if a compaction has been done

When a System.gc() is done with -XX:-UseCMSCompactAtFullCollection, a 
mark-sweep
without compaction is done.  In that instance the call to 
reset_after_compaction() is
not appropriate.

This changeset is built on top of the changeset for 8013032

http://cr.openjdk.java.net/~jmasa/8013184/webrev.00/