Forbid creation of wxStandardPaths object directly.

This happens to work under MSW and Unix where there is only one
wxStandardPaths class for both the console and the GUI applications but
doesn't return the correct result under OS X where the Core Foundation
version, returned by wxStandardPaths::Get(), has to be used for the GUI
programs. And historically this confused a lot of people, so just ensure that
they can't accidentally create an object of the wrong type any more.

Closes #13537.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74428 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/stdpaths.h

@@ -142,9 +142,6 @@ public:
     virtual wxString GetTempDir() const;
 
 
-    // ctor for the base class
-    wxStandardPathsBase();
-
     // virtual dtor for the base class
     virtual ~wxStandardPathsBase();
 
@@ -158,6 +155,10 @@ public:
 
 
 protected:
+    // Ctor is protected as this is a base class which should never be created
+    // directly.
+    wxStandardPathsBase();
+
     // append the path component, with a leading path separator if a
     // path separator or dot (.) is not already at the end of dir
     static wxString AppendPathComponent(const wxString& dir, const wxString& component);
@@ -210,6 +211,12 @@ public:
     virtual wxString GetPluginsDir() const { return m_prefix; }
     virtual wxString GetDocumentsDir() const { return m_prefix; }
 
+protected:
+    // Ctor is protected because wxStandardPaths::Get() should always be used
+    // to access the global wxStandardPaths object of the correct type instead
+    // of creating one of a possibly wrong type yourself.
+    wxStandardPaths() { }
+
 private:
     wxString m_prefix;
 };