Define an AudacityException subclass for file errors

src/FileException.h

@@ -0,0 +1,46 @@
+//
+//  FileException.h
+//  
+//
+//  Created by Paul Licameli on 11/22/16.
+//
+//
+
+#ifndef __AUDACITY_FILE_EXCEPTION__
+#define __AUDACITY_FILE_EXCEPTION__
+
+#include "AudacityException.h"
+#include <wx/filename.h>
+
+class FileException /* not final */ : public MessageBoxException
+{
+public:
+   enum class Cause { Open, Read, Write, Rename };
+
+   explicit FileException
+      ( Cause cause_, const wxFileName &fileName_,
+        const wxString &caption = wxString{},
+        const wxFileName &renameTarget_ = {})
+   : MessageBoxException{ caption }
+   , fileName{ fileName_ }, cause{ cause_ }, renameTarget{ renameTarget_ }
+   {}
+
+   FileException(FileException&& that)
+      : MessageBoxException(std::move(that))
+   {}
+
+   ~FileException() override;
+
+protected:
+   std::unique_ptr< AudacityException > Move() override;
+
+   // Format a default, internationalized error message for this exception.
+   wxString ErrorMessage() const override;
+
+public:
+   Cause cause;
+   wxFileName fileName;
+   wxFileName renameTarget;
+};
+
+#endif