[RP] Ungrab prefix key on layout switch

[Magnus Henoch]

I often switch between QWERTY and Dvorak keyboard layouts (using
setxkbmap).  That means the prefix key (C-t, as default) moves between
two different keys.  ratpoison correctly catches the new prefix key,
but the old one is left unattended - it's neither used by ratpoison
nor sent to applications.  This means that I have to use Emacs without
C-y (Dvorak Y is the same key as QWERTY T).  It would be nice if this
didn't happen...

I'm using ratpoison from CVS, XFree86 4.5.0, NetBSD/macppc 3.99.16.

Magnus