rio: keep bottom'ed windows in order
 [rsc] --rw-rw-r-- M 357477 glenda sys 6169 Mar 10 13:32 sys/src/cmd/rio/data.c
 [rsc] --rw-rw-r-- M 357477 glenda sys 22807 Mar 10 13:32 sys/src/cmd/rio/rio.c
	/n/sourcesdump/2006/0310/plan9/sys/src/cmd/rio/rio.c:517,523 - 
	/n/sourcesdump/2006/0311/plan9/sys/src/cmd/rio/rio.c:517,523
	  					scrolling = mouse->buttons;
	  				else
	  					scrolling = mouse->buttons && ptinrect(xy, winput->scrollr);
	- 				/* topped will be zero if window has been bottomed */
	+ 				/* topped will be zero or less if window has been bottomed */
	  				if(sending == FALSE && !scrolling && winborder(winput, mouse->xy) && winput->topped>0){
	  					moving = TRUE;
	  				}else if(inside && (scrolling || winput->mouseopen || (mouse->buttons&1)))
	/n/sourcesdump/2006/0310/plan9/sys/src/cmd/rio/rio.c:566,572 - 
	/n/sourcesdump/2006/0311/plan9/sys/src/cmd/rio/rio.c:566,572
	  				cornercursor(w, mouse->xy, 0);
	  			/* we're not sending the event, but if button is down maybe we should */
	  			if(mouse->buttons){
	- 				/* w->topped will be zero if window has been bottomed */
	+ 				/* w->topped will be zero or less if window has been bottomed */
	  				if(w==nil || (w==winput && w->topped>0)){
	  					if(mouse->buttons & 1){
	  						;
 [rsc] --rw-rw-r-- M 357477 glenda sys 33362 Mar 10 13:32 sys/src/cmd/rio/wind.c
	/n/sourcesdump/2006/0310/plan9/sys/src/cmd/rio/wind.c:1268,1274 - 
	/n/sourcesdump/2006/0311/plan9/sys/src/cmd/rio/wind.c:1268,1274
	  	if(w!=nil && w->i!=nil && !w->deleted){
	  		bottomwindow(w->i);
	  		flushimage(display, 1);
	- 		w->topped = 0;
	+ 		w->topped = - ++topped;
	  	}
	  }