Install vmod_director

Fixes: #1381
Add a doc paragraph on how and from what varnishncsa produces it's
output.
Rewrite the ban-lurker in light of many changes and evidence that
it basically didn't work as intended any more.
Fix a (very rare) mtx-leak introduced by previous commit.

Spotted by: 	martin

Eliminate some dead code and make sure that the tail-pruner runs,
also when the lurker is busy.
Change "GONE"  bans to "COMPLETED" bans.