Start validating that URLs are full (http:// or https://).

It's too bad we weren't checking for this already - this may
uncover some errors in older scrapers. I'll plan on re-running each
scraper to their oldest year at some point soon, to try and catch them.
Merge pull request #77 from unitedstates/validate_urls

Start validating that URLs are fully qualified
Merge branch 'master' into agriculture