LJ::get_post_ids — Given a user object and some options, return the number of posts or the posts'' IDs (jitemids) that match.
u. A hashref of a row from the user table, sometimes called a "user object". Although only initially a row from the user table, gets a lot of tacked onto it from various other LJ API functions.
opts. 'security' - [public|private|usemask] 'allowmask' - integer for friends-only or custom groups 'start_date' - UTC date after which to look for match 'end_date' - UTC date before which to look for match 'return' - if 'count' just return the count TODO: Add caching?