Comment 13 for bug 1236979

I added the checks for the case where data from a single circ lib is requested. It has increased the speed in this case:

 Function Scan on records_by_item_age "biblio.records_by_item_age" (cost=0.25..10.25 rows=1000 width=16) (actual time=0.853..0.853 rows=1 loops=1)
 Total runtime: 0.865 ms

The commits have been pushed to the collab branch.