cocoa devdraw: activation on receiving Ttop messages

(The new variable "willactivate" is in the input
structure "in", which is illogical.  But this
structure will soon be renamed "app".  I postpone
the renaming to avoid conflicts with simultaneous
Codereview issues.)

R=rsc
CC=plan9port.codebot
http://codereview.appspot.com/5504102

src/cmd/devdraw/cocoa-srv.c

@@ -212,7 +212,7 @@ runmsg(Wsysmsg *m)
 		break;
 	
 	case Ttop:
-	//	_xtopwindow();
+		topwin();
 		replymsg(m);
 		break;