Very few small dance companies celebrate their 30th anniversary twice in one season. Few small dance companies celebrate their 30th anniversary, period. Mortality always threatens in this business. So let us give a shout out to one that survived and prospered. Alonzo King's Lines Ballet opened the second installment of its anniversary festivities Friday evening at Yerba Buena Center for the Arts' Lam Research Theater with a premiere and a mini-retrospective danced by the company's 12 members with an arching physicality and certifiable elan that compensated for a few problematic if not enigmatic moments.