scraper: log.warn -> log.warning

log.warn was an unsupported alias
POST_expando: gracefully fail when called on link with no child.

Previously if POST_expando was called on a link that has no link_child
(i.e. no selftext or media object to show in the expando) it would cause
an exception.

This catches the bad case early and aborts with a 404.
redditfooter: Fix domain comparison for "Powered by reddit" logo.

"myreddit.com" would incorrectly have not shown the license-required
banner.
gold remaining: always show days