Performance crusade in SpecialListredirects:

Performance crusade in SpecialListredirects:
* Use the rd_* fields to build redirect objects directly rather than running additional queries to grab them
** If the rd_* fields are not available (i.e. when running from cache), use Article::getRedirectTarget() rather than grabbing the revision text
* Preload the existence status of the redirects and their targets in a LinkBatch so Linker::link() won't query them one at a time