add some debugging capability for users of SystemExec. Needs review.

libs/ardour/export_handler.cc

@@ -355,15 +355,17 @@ ExportHandler::finish_timespan ()
 			subs.insert (std::pair<char, std::string> ('n', session.name ()));
 
 			ARDOUR::SystemExec *se = new ARDOUR::SystemExec(fmt->command(), subs);
+			info << "Post-export command line : {" << se->GetString() << "}" << endmsg;
 			se->ReadStdout.connect_same_thread(command_connection, boost::bind(&ExportHandler::command_output, this, _1, _2));
-			if (se->start (2) == 0) {
+			int ret = se->start (2);
+			if (ret == 0) {
 				// successfully started
 				while (se->is_running ()) {
 					// wait for system exec to terminate
 					Glib::usleep (1000);
 				}
 			} else {
-				error << "post-export hook failed! " << fmt->command() << endmsg;
+				error << "Post-export command FAILED with Error: " << ret << endmsg;
 			}
 			delete (se);
 		}

libs/pbd/pbd/system_exec.h

@@ -115,6 +115,8 @@ class LIBPBD_API SystemExec
 
 		virtual ~SystemExec ();
 
+		std::string GetString();
+
 		/** fork and execute the given program
 		 *
 		 * @param stderr_mode select what to do with program's standard error

libs/pbd/system_exec.cc

@@ -282,6 +282,18 @@ SystemExec::make_argp_escaped(std::string command, const std::map<char, std::str
 	argp[n] = NULL;
 }
 
+string
+SystemExec::GetString ()
+{
+	stringstream out;
+	if (argp) {
+		for (int i = 0; argp[i]; ++i) {
+			out << argp[i];
+		}
+	}
+	return out.str();
+}
+
 SystemExec::~SystemExec ()
 {
 	terminate ();