8139434: Unify GenRemSet and CardTableRS
Reviewed-by: jwilhelm, mgerdin

8077842: Remove the level parameter passed around in GenCollectedHeap
Reviewed-by: kbarrett, mgerdin

8080112: Replace and remove the last usages of CollectedHeap::n_par_threads()
Reviewed-by: jmasa, kbarrett

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