Change the way the pacing of the ban-lurker is configured.

A new parameter, $ban_lurker_age, sets a minimum age bans must
have before the lurker will touch them.  This way the lurker
stays out of the "rush" that happens right after a ban has been
added.

Another new parameter, $ban_lurker_batch, determines how many
objects the lurker will examine, before it takes a $ban_lurker_sleep
in order to not monopolize CPU.