[9fans] rio support for antialiased fonts

[erik quanstrom]

this is what's needed, if you're interested.

; diff -c /n/sources/plan9/sys/src/cmd/rio .
diff -c /n/sources/plan9/sys/src/cmd/rio/wind.c ./wind.c
/n/sources/plan9/sys/src/cmd/rio/wind.c:709,716 - ./wind.c:709,718
  wrepaint(Window *w)
  {
        wsetcols(w);
-       if(!w->mouseopen)
+       if(!w->mouseopen){
+               draw(w->Frame.b, w->Frame.r, w->display->white, nil, ZP);
                _frredraw(w, w->Frame.r.min);
+       }
        if(w == input){
                wborder(w, Selborder);
                wsetcursor(w, 0);