Try standard XDG location for documents directory

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@53094 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/unix/stdpaths.h

@@ -47,6 +47,9 @@ public:
     virtual wxString GetPluginsDir() const;
     virtual wxString GetLocalizedResourcesDir(const wxString& lang,
                                               ResourceCat category) const;
+#ifndef __VMS
+    virtual wxString GetDocumentsDir() const;
+#endif
 
 private:
     wxString m_prefix;