Respect revisions on hook_cron()

Follow up from #419860: Make feedapi aware of node revisions

This needs to join to node table in order to respect revisions introduced by the patch above.

$result = db_query_range("SELECT DISTINCT nid FROM {feedapi} WHERE next_refresh_time < %d AND next_refresh_time <> %d ORDER BY next_refresh_time ASC", $now, FEEDAPI_CRON_NEVER_REFRESH, 0, FEEDAPI_CRON_FEEDS);