pcache entry ttl handling

Hi,

while working on some issues in slapo-pcache (ITS#6950, 6951, 6953 and 6954). I noticed some (IMO) odd behaviour in how the experiation of cached queries is handled.

It seems that pcache happily returns entries for cached queries from the cache even if the query has already expired (ttl is over). It only stops returning results for such a cached query after the periodic consistency checker has run an removed those expired queries.

If this is really the desired behaviour I think we should clarify this in the man-page. If it's not we should fix the code.