I have committed a change for -multiwindow window manager to the xorg tree. Now the wm should be able to detect another wm and the others can detect it. This change corresponds to the second item (Window manager detection) in the To-Do list.
To do so the internal wm grabs ButtonPressMask, which is allowed only one client at once. Thus other wm's will fail to obtain the mask and immediately exit when invoked. Takuma Murakami
