Increase pitch-shifting quality a bit

OptionPitchHighQuality - Use the highest quality
 method for pitch shifting.  This method has a CPU cost
 approximately proportional to the required frequency shift

gtk2_ardour/editor_timefx.cc

@@ -269,6 +269,8 @@ Editor::time_fx (RegionList& regions, float val, bool pitching)
 	if (longwin)           options |= RubberBandStretcher::OptionWindowLong;
 	if (shortwin)          options |= RubberBandStretcher::OptionWindowShort;
 
+	if (pitching)          options |= RubberBandStretcher::OptionPitchHighQuality;
+
 	switch (transients) {
 	case NoTransients:
 		options |= RubberBandStretcher::OptionTransientsSmooth;