Increase the default value for ht_locks by a factor of approx. 10

Filing this as a bug so it will get noticed and we'll make a decision.

Based on our findings with one of our large customers we may want to consider increasing the default hashtable locks by an order of magnitude to reduce the amount of time sections of the hashtable are locked for any pagers that walk the hashtable checking on items (e.g. access log scanner, item pager, access log scanner, etc.)

My suggestion would be to increase ht_locks to 53 or 47 (prime numbers are a good idea according to Chiyoung.)