fixup 'rename team::is_human -> is_local_human'
fix "player_id" during mp_connect/mp_wait

the value of "player_id" is only used to set the userlist in mpwait in
case there is no other userlist available (usualy there is another list
available) adding a side number doesn't make sense.

We also use a std::set for gathering the player_id values to make sure
there is no player_id twice.