Screensaver lock by-pass via the virtual keyboard

See also: https://www.jwz.org/xscreensaver/toolkits.html

> I wrote this document in 2004, explaining the approach to privilege separation that xscreensaver has taken since 1991. Of course, the people doing needless rewrites of xscreensaver have ignored it for that whole time, and have then gone on to introduce exactly the bug that I described in this document as a hypothetical strawman!