This implementation is simpler to understand. It
removes conflicts with other modifiers and with
the virtual buttons. Pressing alt during a
sequence now cancels it correctly.
R=rsc
CC=plan9port.codebot
http://codereview.appspot.com/5507049
(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
