Get rid of the curses keyboard incapabilities

qemu's curses display driver messes the keys up that are sent to my kernel
through qemu. It makes me unable to receive proper Esc - which is normal for
any (n)curses program -, Break, SysRq, etc. keys and Ctrl, Alt, etc. in
general because they're sent just in time which is not the case for real
hardware.

The only solution I see is to use the sdl driver with its fbcon driver. This
requires some good amount tweaking to get convenient. That much that I
renamed 'run' to 'myrun' because it is now even more tailored to my setup.

We need two ttys. The first one hosts the qemu display for the sdl fbcon.
The second gets the qemu console for debugging purposes. We must redirect a
tty owned by us (if we're in a PTY session which I normally am), i.e. tty1
on my system normally, to the openvt program to get the first new tty. The
second tty can be our pty itself. We end up with a fully usable virtual
machine with a sane keyboard emulation somewhere around tty7 or tty8 and the
qemu console in the pty we started "make myrun" from.

The function ensure_tty was added to somehow own a tty permanently. It only
disturbs once. The "stty echo" seems needed as openvt does not exit cleanly
on my system (or it is the qemu console that mucks up)...

I also added the -no-reboot option because the first thing I'll now
implement will be Ctrl+Alt+Del to reboot which will then shutdown the
emulator and bring us back the pty we started from. (Yeah, very funny that I
recently rebooted my machine accidentally by playing around with this
combination ;-))

Altogether less convenient than the curses interface but more correct.

At least, I don't have to change the interface key combinations and can
write a proper keyboard driver with right scancodes now.