State partitioning anomaly

• Adding get2 --- variant of get that obtains two values at once

  bbuf2 = interface { empty, one, mid, full }
      extends bbuf { mid } becomes { one, mid }
    get2 = method({mid}b:self{mid,one,empty}) replies(int,int)
  end bbuf2
  bbuf2i = class implements bbuf2 extends bbuf_basei
      after get{mid}, put{mid} use setstate
    get2 = method({mid}b:self{mid,one,empty}) replies(int,int)
      b.opt := (b.opt+1)//b.size; v1:int := b.arr[b.opt]
      b.opt := (b.opt+1)//b.size; v2:int := b.arr[b.opt]
      b.cnt := b.cnt-2; b!setstate(); reply(v1, v2)
    end get2
    setstate = method(b:self)
      if b.cnt = b.size then b!{full}
      elseif b.cnt = 0 then b!{empty}
      elseif b.cnt = 1 then b!{one}
      else                  b!{mid} end
    end setstate
  end bbuf2i