8155233: Lazy coarse map clear Summary: Only clear the coarse bitmaps of the remembered sets if they were dirtied. Reviewed-by: jmasa, mgerdin

8155230: Tune thread usage for mark bitmap clear Reviewed-by: jmasa, mgerdin

8153507: Improve Card Table Clear Task Summary: Move card table clear code into remembered set related files. Improve work distribution of this task, and tune thread usage. Reviewed-by: jmasa, mgerdin