and try to push objects away from the tail end so that the list
can be shortened.

It won't work if your bans contains any req.* tests, because the
lurker has no request to compare against.

By default the lurker is disabled, you enable it by setting the
'ban_lurker_sleep' parameter to the amount of time the lurker
should sleep between doing things.

If it cannot do anything, it always sleeps for a second.

NB: This feature is on probation, there is currently no guarantee
it will end up in a future varnish release, it depends on the
impact and usability.  Feedback much anticipated.


One of the quasi-nasty details of this feature, is the need to work
against the lock-order in cache_hash.c, see details in comments for
HSH_FindBan().




git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@4206 d4fa192b-c00b-0410-8231-f00ffab90ce4