revert region optimization to create_atoms

  domain->lattice->bbox(1,bboxhi[0],bboxhi[1],bboxhi[2],

                        xmin,ymin,zmin,xmax,ymax,zmax);

  // narrow down min/max further by extent of the region, if possible

  if ((style == REGION) && domain->regions[nregion]->bboxflag) {

    double rxmin = domain->regions[nregion]->extent_xlo;

    double rxmax = domain->regions[nregion]->extent_xhi;

    double rymin = domain->regions[nregion]->extent_ylo;

    double rymax = domain->regions[nregion]->extent_yhi;

    double rzmin = domain->regions[nregion]->extent_zlo;

    double rzmax = domain->regions[nregion]->extent_zhi;

    domain->lattice->box2lattice(rxmin,rymin,rzmin);

    domain->lattice->box2lattice(rxmax,rymax,rzmax);

    if (rxmin > xmin) xmin = (rxmin > xmax) ? xmax : rxmin;

    if (rxmax < xmax) xmax = (rxmax < xmin) ? xmin : rxmax;

    if (rymin > ymin) ymin = (rymin > ymax) ? ymax : rymin;

    if (rymax < ymax) ymax = (rymax < ymin) ? ymin : rymax;

    if (rzmin > zmin) zmin = (rzmin > zmax) ? zmax : rzmin;

    if (rzmax < zmax) zmax = (rzmax < zmin) ? zmin : rzmax;

  }

  // ilo:ihi,jlo:jhi,klo:khi = loop bounds for lattice overlap of my subbox

  // overlap = any part of a unit cell (face,edge,pt) in common with my subbox

  // in lattice space, subbox is a tilted box