Fix miniwindows auto-arranging bug

Fix miniwindows auto-arranging bug

With this patch, minimized windows do not reshuffle anymore.

See http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=361241
where Martin Hinsch reported:

"The behaviour of icons (minimized applications) is severely broken when
 automatic placement is switched on.
  * When switching the workspace icons often stick thereby covering (and
    hiding) icons on the workspace one is switching to.
  * After minimizing an application, clicking (singly or doubly) on one of
    the icons causes all of them to reshuffle, usually in a way that the
    icon in question changes its place (which is extremely annoying).
  * Icon placement ignores the dock so that icons disappear behind
    it/cover it.

 All of these suddenly appeared about a year ago (I think with 91.0). The
 problems are not architecture-specific since they occur in exactly the
 same way on my pentium machine. Wiping the complete configuration (rm -r
 ~/GNUstep) did not make a change either."