Attempt to make wxCompositeWindow<> compile with MSVC6.

Blind attempt to work around VC6 error about ambiguity between "const T&" and
"T" in DoSetForAllParts() template function.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66580 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/compositewin.h

@@ -90,7 +90,7 @@ private:
     virtual wxWindowList GetCompositeWindowParts() const = 0;
 
     template <class T>
-    void DoSetForAllParts(bool (wxWindowBase::*func)(const T&), const T& arg)
+    void DoSetForAllParts(bool (wxWindowBase::*func)(const T&), T arg)
     {
         // Simply call the setters for all parts of this composite window.
         const wxWindowList parts = GetCompositeWindowParts();