6624765: Guarantee failure "Unexpected dirty card found"
Summary: In verification take into account partial coverage of a region by a card and expansion of the card table.
Reviewed-by: ysr, apetrusenko
6659981: +ParallelRefProcEnabled crashes on single core platform
Summary: Disable parallel reference processing when there are no worker threads
Reviewed-by: apetrusenko, pbk, jmasa, tonyp