Combined struct llist and struct mlist into superset struct ulist.

Combined struct llist and struct mlist into superset struct ulist.
(assa, set_leader, switch_leader, set_flagship, switch_flagship,
take_move_in_mob, get_land, ask_olist, att_get_defense,
get_dlist, get_ototal, get_dtotal, kill_land, att_infect_units,
put_land, att_reacting_units, count_bodies, att_fight,
send_reacting_units_home, take_def, ask_move_in, move_in_land,
lnd_print, lnd_delete, lnd_take_casualty, lnd_takemob,
lnd_sel, lnd_mar, lnd_put, lnd_sweep, contains_engineer,
lnd_check_mines, lnd_list, lnd_mess,
lnd_damage, lnd_easiest_target, lnd_mar_one_sector, shp_sel,
shp_nav, shp_put, shp_sweep, shp_check_one_mines, shp_check_mines,
shp_list, shp_mess, shp_count, shp_damage_one, shp_damage,
shp_contains, most_valuable_ship, shp_easiest_target,
shp_missile_interdiction, notify_coastguard,
shp_view, shp_nav_one_sector, shp_missdef, nav_ship,
fltp_to_list): Switch to struct ulist from either struct mlist
or struct llist.