8152182: Possible overflow in initialzation of _rescan_task_size and _marking_task_size
Summary: Add constraints for CMSRescanMultiple and CMSConcMarkMultiple flags
Reviewed-by: jwilhelm, jmasa
8152180: SIGFPE in CMSCollector::preclean with big CMSScheduleRemarkSamplingRatio
Summary: Rephrased the calculation routine to avoid an overflow for CMSScheduleRemarkSamplingRatio
Reviewed-by: jwilhelm, drwhite