LJ::join_community — Makes a user join a community. Takes care of all reluser and friend stuff.
LJ::join_community(uuserid, ucommid, friend, noauto);
uuserid. a userid or u object of the user doing the joining
ucommid. a userid or u object of the community being joined
friend. 1 to add this comm to user's friends list, else not
noauto. if defined, 1 adds P edge, 0 does not; else, base on community postlevel
1 if success, undef if error of some sort (ucommid not a comm, uuserid already in