Undo.h: Lots of warnings about non-virtual destructor
When I build MuseScore from SVN trunk the compiler emits lots of warnings against most (if not all) of the classes in undo.h, inheriting from UndoCommand. "the class ... has virtual functions but non-virtual destructor".
As far as I can see this has a really easy fix - add the virtual keyword to the destructor of UndoCommand.
I have attached a patch.