os is a nickname of the posix package but it was breaking with -K full on gentoo.
Add a workaround for xlib:wm-class
In both the clisp and sbcl clx libraries, sometimes in te event slots, what should be a window will be a pixmap instead. In this case, we need to manually translate it to a window to avoid breakage in stumpwm. So far the only slot that seems to be affected is the :window slot for configure-request and reparent-notify events. It appears as though the hash table of XIDs and clx structures gets out of sync with X or perhaps X assigns a duplicate ID for a pixmap and a window. Since I haven't found a way to reliably reproduce this bug, this code is untested.