The saver itself then will use a subwindow of the grab_window. End
result: in case the saver calls XUngrabKeyboard on the window it's told,
it no longer will stop our grab. The "bumps" XScreenSaver hack does
exactly this.

With this, I also could remove the previously existing hack to reinstate
the grab every 100ms.

This makes the behavior of pressing a key while the saver is running
more intuitive.

Sorry for that. After this, unlocking properly authenticates again.

Use this if you for some reason can't use PAM.

This will ask for a new password if the user's password has expired
before unlocking.

As with XScreenSaver, checking for its return value needs to be
explicitly enabled via --enable-pam-check-account-type.

A random byte in memory was set to 0 in auth_pam_x11, and the password
possibly not zero terminated.

Thanks, Coverity!

Usage: --with-pam-service-name=xscreensaver.

This partially mitigates leakage of passwords to swap.

Note that information about the password from the X11 event queue, as
well as leakage on suspend-to-disk, may still be leaked.

Document the reasons why we don't endless loop here, as this password
buffer code may otherwise be too hard to follow.