s3-prefork: better timing out semantics

s3-prefork: better timing out semantics

If this child has no clients, let the lock functions block for 1 second,
and then immediately reschedule the operation. This means we catch the lock
as soon as possible on a free child.

If, instead, we are already serving a client, we want to be non blocking,
so we timeout immediately on getting the lock, and then we sleep a 1/10th of
a second.
This means that a busy child will be slightly slower on picking up the lock,
but we won't block the existing client from communicating with us as we
immediately react to activity on the already opened file handler.

Signed-off-by: Andreas Schneider <asn@samba.org>