asynchronously, in the same style like the process attach/detach functions
-intercept the "cnpollc" call which originally went directly to the
keyboard driver and keep track whether the console is in "polling" state
(DDB!)
-pass a NULL callback to the screen switcher and the process attach/detach
functions if the console is "polling", to tell them that asynchronous
completion is forbidden
and one which isn't. The latter is now used for ttyEcfg, enabling the
VT-switching ioctls to work on it. (This allows Linux X servers to work when
/emul/linux/dev/tty0 is linked to /dev/ttyEcfg.)
1. If the current screen becomes invalid (ie no focus anymore), always
set the keyboard to translating mode. Otherwise, we could get stuck
because the command keystokes don't come through.
2. Catch errors in attaching to a process (X server) - For this,
implement a callback mechanism similar to the detach case. Add an
argument to report an errno via callback.
drochner