Rename leaderboard user_id parameter to user_ids for accuracy
phpDoc corrections
Make leaderboard_query variable to be an ArrayObject to avoid pass-by-ref errors caused by the magic getter
Add new function to return correct page number for leaderboard pagination

If a top-level /leaderboard/ rewrite is ever added, we can make this
properly use query vars and rewrite rules.
Use leaderboard paged helper in dpa_get_leaderboard
Another ArrayObject reference missed in df7996209e4e8a
First pass at dpa_has_leaderboard() template function