In order to do this we have to plumb it through the queue and the
Handler interface, but it should allow fetches of the resources
associated with a page via the IncludeRelatedScope even if it's behind
a redirect.

Detect write errors (both on the database and to the WARC output) and
abort with an error message.

Also fix a bunch of harmless lint warnings.

The native Go implementation of LevelDB.

The queuing code now performs proper lease accounting, and it will not
return a URL twice if the page load is slow.