[Exim] No locking problem for hints databases

Hello,

a short while ago I wondered how much avoiding hints databases would
gain to speed up local deliveries, where hints are stored on tmpfs.
I measured how long Exim has to wait for the DB lock and found out,
that even with about 20 queue runners working on a queue of about 5000
mails, the lock could mostly be taken without measurable delay, a very
few times the delay was 10ms and just once it was higher: 140 ms.

So the answer for my systems is: Avoiding the hints DB would not help
at all.

Michael