Correctly terminate plasp with failure exit code when unhandled exceptions are caught.

apps/plasp-app/main.cpp

@@ -71,7 +71,7 @@ int main(int argc, char **argv)
 		{
 			std::cerr << messagePrefix << ": " << exception.what() << std::endl << std::endl;
 			printHelp();
-			return EXIT_FAILURE;
+			exit(EXIT_FAILURE);
 		};
 
 	try