Add charset support to wxLocaleIdent and accessors

Charset is important for Unix systems as some locales may not be
available without it, e.g. "xx_XX" may not be supported, but
"xx_XX.utf8" could be.

src/unix/uilocale.cpp

@@ -67,6 +67,9 @@ wxString wxLocaleIdent::GetName() const
         if ( !m_region.empty() )
             name << "_" << m_region;
 
+        if ( !m_charset.empty() )
+            name << "." << m_charset;
+
         if ( !m_modifier.empty() )
             name << "@" << m_modifier;
     }