COW cleanup patch (1583966):

1. perform deep comparison for the classes for which it makes sense in the
   ports where this wasn't done yet
2. remove (shallow) comparison operators for the classes for which it does
   not make sense (such as wxBitmap)
3. makes wxBitmap use COW on all ports
4. adds wxObject::IsRefTo()
5. centralizes and improves COW docs


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42752 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/image.h

@@ -392,11 +392,6 @@ public:
     // -1.0..1.0 where -1.0 is -360 degrees and 1.0 is 360 degrees
     void RotateHue(double angle);
 
-    bool operator == (const wxImage& image) const
-        { return m_refData == image.m_refData; }
-    bool operator != (const wxImage& image) const
-        { return m_refData != image.m_refData; }
-
     static wxList& GetHandlers() { return sm_handlers; }
     static void AddHandler( wxImageHandler *handler );
     static void InsertHandler( wxImageHandler *handler );