MIDI robustness.

- Separate SMF::open and SMF::create, more powerful interface for both.
- Correctly handle note ons with velocity 0 as note offs in sequence.
- Use SMF (i.e. libsmf) for MIDI import


git-svn-id: svn://localhost/ardour2/branches/3.0@4558 d708f5d6-7413-0410-9779-e7cbd77b26cf

libs/ardour/smf_source.cc

@@ -65,7 +65,7 @@ SMFSource::SMFSource (Session& s, std::string path, Flag flags)
 		throw failed_constructor ();
 	}
 	
-	if (open(path)) {
+	if (create(path)) {
 		throw failed_constructor ();
 	}