Bug2135: startup should not fail quietly when audacity.cfg is locked...

simplest fix is simply to put up a message box explaining it

src/Prefs.cpp

@@ -61,6 +61,7 @@
 #include <wx/stdpaths.h>
 
 #include "FileNames.h"
+#include "Internat.h"
 #include "MemoryX.h"
 #include "Languages.h"
 
@@ -220,6 +221,20 @@ void InitPreferences()
    wxConfigBase::Set(gPrefs);
 }
 
+bool CheckWritablePreferences()
+{
+   return gPrefs->Write("/TEST", true) && gPrefs->Flush();
+}
+
+wxString UnwritablePreferencesErrorMessage()
+{
+   wxFileName configFileName(FileNames::DataDir(), wxT("audacity.cfg"));
+   return wxString::Format(
+     _("Audacity cannot start because the settings file at %s is not writable."),
+     configFileName.GetFullPath()
+   );
+}
+
 void FinishPreferences()
 {
    if (gPrefs) {