[wmii] Enable ARGB visual for wmii frame

Hi,

I'd like to use the alpha channel for setting real transparency of my
terminal's background (rxvt-unicode), which is much better than just
making the whole window transparent, since with ARGB support one can
have a transparent background, but non-transparent text (like with
pseudo transparency, but much cleaner and better working).

May I quote an irc discussion how easy one can add support for the ARGB
visual in a window manager:
------------
     lack| I've got real transparency working in beryl, but I hate beryl, so I want
           to figure out how to hack fluxbox to do the proper magic so I can get
           real transparency to work there too. In the man page it says: ...but
           that doesn't mean that your WM has the required kludges in place. Where
           can I learn more about these kludges?
     lack| I should add: real transparency using an ARGB visual.
  schmorp| seriously, wyh don't you use a standalone compositing manager such as
           xcompmgr?
   dyfrgi| Beryl is a composite manager, not just a window manager.
  schmorp| or beryl, or fvwm, or...
     lack| xcompmgr doesn't seem to enable ARGB in fluxbox.
  schmorp| the bug with the design of all that
     lack| I think I need fluxbox to do something "special" but I don't know what
           that is.
  schmorp| is that it requires changes to all apps
  schmorp| if fluxbox has window decorations
  schmorp| and works by reparenting
  schmorp| then the outer window must be argb, too
  schmorp| i ince wrote a patch against fvwm
  schmorp| http://data.plan9.de/fvwm-2.5-argb-visual.patch
     lack| Cool.
  schmorp| which basically gives windows the "right" visual
  schmorp| note:
  schmorp| if (fw->attr_backup.visual->class == TrueColor
  schmorp| + && fw->attr_backup.depth == 32)
  schmorp| +this is one of the most atrocious hacks i ever wrote
  schmorp| because 32 bpp does not mean argb
  schmorp| but there is *no* way to test for argb
-------------

It would be nice, if one can add this support to wmii (3.5 or 3.7), it
wouldn't take much code, but ARGB visual opens a lot of possibilities
for applications which use it.

--
Martin