correct out-of-bounds array access in RanMars::select_subset()

  int mode,index,oldindex,newvalue,nflip,which,niter;

  int active[2],first[2],last[2];

  int newactive[2],newfirst[2],newlast[2];

  bigint nmark,nactive,nactiveall,nflipall,bnflip;

  bigint activeall[2],bsum[3],bsumall[3];

  bigint nmark,nactive,nactiveall,nflipall;

  bigint activeall[2],bsum[4],bsumall[4];

  double thresh;

  active[0] = nmine;