put patch chnage dialog under the mouse cursor when it appears

git-svn-id: svn://localhost/ardour2/branches/3.0@12914 d708f5d6-7413-0410-9779-e7cbd77b26cf

gtk2_ardour/midi_region_view.cc

@@ -3737,6 +3737,9 @@ void
 MidiRegionView::edit_patch_change (ArdourCanvas::CanvasPatchChange* pc)
 {
 	PatchChangeDialog d (&_source_relative_time_converter, trackview.session(), *pc->patch (), instrument_info(), Gtk::Stock::APPLY);
+
+        d.set_position (Gtk::WIN_POS_MOUSE);
+
 	if (d.run () != Gtk::RESPONSE_ACCEPT) {
 		return;
 	}