From: Samuel Thibault <Samuel.Thibault@ens-lyon.fr>

Still working on kernel facilities for braille devices, the need for being
able to force blanking and unblanking raised: even when a key is pressed, the
screen must remain blank, for privacy of the blind user who is typing on the
keyboard and reading on its braille terminal.

I merely added an ignore_poke variable which is set, and the screen blanked.
Then, poke_blanked_console returns immediatly.  Upon real unblank (because of
an Oops or an explicit tioclinux), ignore_poke is reset to get back to normal
operation mode.

I had to remove the (unnecessary ?) call to unblank_screen from set_selection
to prevent mouse selection unblanking the screen.

I also added a way for processes to know whether the screen is blanked (the
blind user might hence know whether people can read the screen).