Upgrade WX to r74856, mainly to support @2x.

Externals/wxWidgets3/include/wx/weakref.h

@@ -3,7 +3,6 @@
 // Purpose:     wxWeakRef - Generic weak references for wxWidgets
 // Author:      Arne Steinarson
 // Created:     27 Dec 07
-// RCS-ID:      $Id: weakref.h 67280 2011-03-22 14:17:38Z DS $
 // Copyright:   (c) 2007 Arne Steinarson
 // Licence:     wxWindows licence
 /////////////////////////////////////////////////////////////////////////////
@@ -227,14 +226,14 @@ public:
     template <class TDerived>
     wxWeakRef(TDerived* pobj)
     {
-        Assign(pobj);
+        this->Assign(pobj);
     }
 
     // We need this copy ctor, since otherwise a default compiler (binary) copy
     // happens (if embedded as an object member).
     wxWeakRef(const wxWeakRef<T>& wr)
     {
-        Assign(wr.get());
+        this->Assign(wr.get());
     }
 
     wxWeakRef<T>& operator=(const wxWeakRef<T>& wr)