we used to bind a pipe to /dev/cons and /dev/consctl with some
shared segment hack to pass tty info arround. now we implement
this as a fileserver.
add support for "winchon"/"winchoff" ctl message to enable interrupt
on window size change. (used by ssh)
keep track of fullscreen scrolls, avoiding redrawing the whole
screen each time.
the event library doesnt do any flow control. if the host
keeps sending data while the user is mousing arround,
extract() will collect the data until memory fills up.
so instead we abandon the event library and convert
the program to use channels.
