devdraw: fix title and "open in top" on OS X

On OSX 10.10, when you open an application that depends on devdraw, the
title bar only shows the first letter of the application's name. The
patch sets a default title as soon as the window is created, which
fixes this issue.

On OSX 10.10, when you open an application that depends on devdraw, this
application is opened in top of other windows, however the menu bar is
not updated. The patch calls topwin() at the end of makewin() in
src/cmd/devdraw/cocoa-screen.m .

Change-Id: Ie036928b5574c8df20ad8b2b54047e2f7a22bb41
Reviewed-on: https://plan9port-review.googlesource.com/1091
Reviewed-by: Russ Cox <rsc@swtch.com>