Add relavent OSX midi options in the startup dialog

- MIDI driver options are now "None" and "coremidi" on OSX
- If coremidi is selected, jack will start with midi activated
- Requires Jack OSX version 0.90 beta 15 (or another version that
  supports midi

gtk2_ardour/engine_dialog.cc

@@ -167,8 +167,12 @@ EngineControl::EngineControl ()
 
 	strings.clear ();
 	strings.push_back (_("None"));
+#ifdef __APPLE__
+	strings.push_back (_("coremidi"));
+#else
 	strings.push_back (_("seq"));
 	strings.push_back (_("raw"));
+#endif
 	set_popdown_strings (midi_driver_combo, strings);
 	midi_driver_combo.set_active_text (strings.front ());
 
@@ -439,6 +443,12 @@ EngineControl::build_command_line (vector<string>& cmd)
 
 	cmd.push_back ("-T"); // temporary */
 
+	/* setup coremidi before the driver, otherwise jack won't start */
+
+	if (midi_driver_combo.get_active_text() == _("coremidi")) {
+		cmd.push_back ("-X coremidi");
+	}
+
 	/* next the driver */
 
 	cmd.push_back ("-d");