Settings management: try to fix full filename issues when using non ASCII7 chars.

The fix convert all std::string storing a path to wxString (unicode support)
wxString were already used at many place to store paths, but not all.
For internal calculations mixing char strings and wide char strings is a recipe
for bug: any missing conversion between UTF8 and wxString breaks paths.

common/settings/nested_settings.cpp

@@ -41,7 +41,7 @@ NESTED_SETTINGS::~NESTED_SETTINGS()
 }
 
 
-bool NESTED_SETTINGS::LoadFromFile( const std::string& aDirectory )
+bool NESTED_SETTINGS::LoadFromFile( const wxString& aDirectory )
 {
     clear();
     bool success = false;
@@ -75,7 +75,7 @@ bool NESTED_SETTINGS::LoadFromFile( const std::string& aDirectory )
 }
 
 
-bool NESTED_SETTINGS::SaveToFile( const std::string& aDirectory, bool aForce )
+bool NESTED_SETTINGS::SaveToFile( const wxString& aDirectory, bool aForce )
 {
     if( !m_parent )
         return false;