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
3 files changed