Refactor code finding the name of the windows class to use in wxMSW

Determine which class name to use in MSWCreate() caller instead of doing it
partly there and partly in MSWCreate() itself, which used to add the "NR"
suffix if necessary -- now it doesn't do this any more and just really created
the window using the given class.

No real changes, just prepare for future enhancements.

include/wx/msw/window.h

@@ -230,8 +230,11 @@ public:
     // get the HWND to be used as parent of this window with CreateWindow()
     virtual WXHWND MSWGetParent() const;
 
-    // get the Win32 window class name used by all wxWindow objects by default
-    static const wxChar *MSWGetRegisteredClassName();
+    // Return the name of the Win32 class that should be used by this wxWindow
+    // object, taking into account wxFULL_REPAINT_ON_RESIZE style (if it's not
+    // specified, the wxApp::GetNoRedrawClassSuffix()-suffixed version of the
+    // class is used).
+    const wxChar *GetMSWClassName() const;
 
     // creates the window of specified Windows class with given style, extended
     // style, title and geometry (default values