LJ::get_postto_list — Get the list of usernames a given user can post to.
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. Optional hashref. keys are: - type: 'P' to only return users of journaltype 'P'. - cap: cap to filter users on.