insert_before( child1, child2 )
  
	Instance Public methods
	Inserts an child before another child @param child1 this is either an xpath
or an Element.  If an Element, child2 will be inserted before child1 in
the child list of the parent. If an xpath, child2 will be inserted before
the first child to match the xpath. @param child2 the child to insert
@return the parent (self)