A scoped_ptr would be more suitable and efficient but scoped_ptr doesn't support
a custom deleter function(sf_close in this case), there are ways around that
limitation but I don't think it is worth doing at this point as it requires more
code etc.
git-svn-id: svn://localhost/ardour2/trunk@2656 d708f5d6-7413-0410-9779-e7cbd77b26cf