grid_move_cells
grid_move_cells(gd, px + nx, px, py, sx - px - nx, bg);
grid_move_cells(gd, px, px + nx, py, sx - px - nx, bg);
grid_move_cells(gd, 0, want, yy + lines, left, 8);
void grid_move_cells(struct grid *, u_int, u_int, u_int, u_int, u_int);