6997298: fatal error: must own lock CMS_markBitMap_lock during heap dump Summary: Since we are at a stop-world pause, the existing CMS-phase checks are sufficient for safety, and the locking check can be safely elided. Elaborated documentation comment to the case where class unloading and verification are disabled, and the query happens when we aren't in the sweeping phase, where the answer "false" would be (almost everywhere) too pessimistic. Reviewed-by: jmasa, johnc, tonyp