Exclusive window manager for -multiwindow

[Takuma Murakami]

Harold,

>   I tested your fix and it works fine with twm.  Doing a 'startkde' on a 
> remote box does not fail like twm does... it still works and has weird 
> behavior.  I wonder if there is something else that we need to do to 
> work with modern window managers?  In any case, your fix is better than 
> what we had before.  :)

Yes, it works only for twm and those who inherit twm's code
(e.g. wmaker).  The default window manager for KDE, kwin, uses
SubstructureRedirectMask for wm detection.  However we cannot
do just grabbing the mask, unlike ButtonPressMask for twm.
For the mask it is necessary to properly handle three requests
dispatched by the mask in winMultiWindowXMsgProc.

It may or not may be a little work, but what I'm really afraid
of is that win32rootless combined with XWinWM could have
already implemented it, though I don't know.  I must avoid
to make things duplicate.

Takuma Murakami