r21810: - The height of a widget is in relation to its enclosing widget. Specifying a

r21810: - The height of a widget is in relation to its enclosing widget.  Specifying a
  height of 100% means that if the enclosing widget is 100 pixels high, this
  widget should be 100 pixels high.  If this widget is then placed someplace
  other than at the top of the enclosing widget, e.g. with top:20, the bottom
  of this widget will fall off the bottom of the enclosing widget.

  The normal way to solve this is to specify top and bottom attributes rather
  than top and height attributes.  Also, since widgets often look better if
  they don't extend all the way to the very bottom, specifying a bottom
  attribute equal to the top attribute typically has an appealing appearance.

  I've fixed the tree widget so it no longer falls off the bottom of the page.
(This used to be commit 44d5f5ec6db76c981f94e7322f82592e5d85be9f)