Followup to r51583: actually use the rd_interwiki and rd_fragment fields, in the...

Followup to r51583: actually use the rd_interwiki and rd_fragment fields, in the spirit of r33133: we now use the redirect table as a cache for redirect targets, no longer pulling the page text from ES for every logged-in redirect view. Old-style redirect table entries with NULL for fragment and interwiki are automatically updated when the redirect is visited or edited.