xrandr: get gamma and brightness

xrandr: get gamma and brightness

Even in verbose query mode, gamma and brigthness were not displayed.
That's because they are not stored in the server the same way they are
specified on the command line: they are stored as 256 * 3 u16 while
the command line is 3 + 1 floats.  Still, this is useful info for the
users, and they don't care about how it's stored in the server.

So we do a regression over the values stored to recover info in the same
way as on the command line: gamma and brightness.

Signed-off-by: Éric Piel <eric.piel@tremplin-utc.net>
Reviewed-By: Matthias Hopf <mhopf@suse.de>