Define an AudacityException subclass for user cancellation of progress

src/UserException.cpp

@@ -0,0 +1,24 @@
+//
+//  UserException.cpp
+//  
+//
+//  Created by Paul Licameli on 11/27/16.
+//
+//
+
+#include "Audacity.h"
+#include "UserException.h"
+
+UserException::~UserException()
+{
+}
+
+std::unique_ptr< AudacityException > UserException::Move()
+{
+   return std::unique_ptr< AudacityException >
+   { safenew UserException{ std::move( *this ) } };
+}
+
+void UserException::DelayedHandlerAction()
+{
+}