relayout() is almost an infinite loop. Instead, only call startAnimation()
when an item has actually been added or removed.
svn path=/trunk/KDE/kdebase/workspace/libs/plasma/; revision=748736
* introduce relayout() which does only that
* place guards around relayout() calls in Layout class to prevent recursion
svn path=/trunk/KDE/kdebase/workspace/libs/plasma/; revision=738923