The Finder can be reactivated after Devdraw's activation if both windows are on the same space. We prevent this by preventing Plumb.app's activation in the first place. R=rsc CC=plan9port.codebot http://codereview.appspot.com/5498096
R=rsc CC=plan9port.codebot http://codereview.appspot.com/5434052
R=rsc http://codereview.appspot.com/4113042
R=rsc http://codereview.appspot.com/2783041