Rename Mac wxCursor::CreateFromImage() to InitFromImage()

Use the same name as in the other ports for the function doing the same
thing, there doesn't seem to be any good reason to name it differently.

Also avoid declaring it when wxUSE_IMAGE==0 as it's not defined in this
case (again, consistently with the other ports).

include/wx/osx/cursor.h

@@ -44,7 +44,9 @@ protected:
 private:
     void InitFromStock(wxStockCursor);
 
-    void CreateFromImage(const wxImage & image) ;
+#if wxUSE_IMAGE
+    void InitFromImage(const wxImage & image) ;
+#endif // wxUSE_IMAGE
 
     wxDECLARE_DYNAMIC_CLASS(wxCursor);
 };