Heritrix: Internet Archive Web Crawler

Current frontier report has no spot for 'finished'
queues -- those that had been created but currently
have no items. This probably traces back to (1)
previous frontiers didn't keep these empty queues
around; (2) they're not guaranteed finished, just
'finished as far as we know right now, pending future
discoveries'.

Now with 1.4's bdb-backed map we can have those empty
queues paged out to disk, so can keep them around. (You
can deduce how many there are in current reports by
taking total queues and subtracting
active+inactive+retired.)

So, there should be a readout of how many are in this
state. But, let's call them 'exhausted' to avoid any
unintended implication that the queue is done for good.