Fix for TextCtrl problem as reported by Vegh

Move definition of wxMenuItem to /gtk/menuitem.h
  Radical change of how to insert a child into a
    paren window. As C++ doesn't have any VMT in
    a class's consructor, I have to use a callback.
  Fixed culumn resizing bug in wxListCtrl
  Fixed menu height bug in MDI code


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@955 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/slider.cpp

@@ -99,10 +99,13 @@ bool wxSlider::Create(wxWindow *parent, wxWindowID id,
   SetRange( minValue, maxValue );
   SetValue( value );
   
+  m_parent->AddChild( this );
+
+  (m_parent->m_insertCallback)( m_parent, this );
+  
   PostCreation();
   
   SetBackgroundColour( parent->GetBackgroundColour() );
-  SetForegroundColour( parent->GetForegroundColour() );
 
   Show( TRUE );