vt: Emulate \e[100-107m (bright background colors).

For now, these fall back to regular (dark) colors.

It'd be tempting to replace blink with bright backgrounds, as permitted by
CGA/VGA -- we already muck with the other programmable bit (foreground
brightness vs 512 character font).  This would bring vgacon in line with
fbcon, which doesn't support blink anywhere but on some drivers renders
that bit as bright background.  If that is done, this commit should be
amended to be one of ways of setting that bit.

Signed-off-by: Adam Borowski <kilobyte@angband.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>