change slides the old desktop out and the new one in. Should not
be really technically different from the cube.
svn path=/branches/work/kwin_composite/; revision=629163
instances and keeping them around after the window is closed, create
class Deleted as a representation of a closed window.
(Why do I always forget 'svn add'?)
svn path=/branches/work/kwin_composite/; revision=626357