xlock and logout button

[Urs Thuermann <urs@isnogud.escape.de>]

since my last aptitude upgrade, xlock shows a logout button 10 minutes
after having locked my Xserver.  I think this is a new feature since I
don't remember having seen this behavior before.

I haven't found a way to disable the appearance of the logout button,
neither in the man page nor in /etc/X11/app-defaults.  How can I
disable this button?  I need this for a non-public terminal in my
bureau where I often lock the screen for longer than 10 minutes, going
to lunch or even over night.

urs