Using tty1 instead of tty0

[Samuel Thibault <sthibault@debian.org>]

Hello,

While trying to fix #998424 (making steps interruptible in the text
frontend), I realize than the debian installer main menu is running
on /dev/tty0, which makes it insensible to ^C etc. That's not really
a problem for the newt frontend, but it prevents from using it for
interruptible steps in the text frontend, and what's worse, it prevents
from using it when running a shell from the main menu, making the shell
there really inconvenient.

I have thus pushed a fix in rootskel to make it open /dev/tty1 instead
of /dev/tty0, which I think won't have consequences beyond proper signal
handling, since they're essentially the same except for tty handling.

Just wanted to raise the flag in case somebody sees anything that could
go wrong with it (tty/signal handling by itself shouldn't be a concern
since that's what we already have when running on a serial console etc.)

Samuel