the code

    try:
        root = self._getRoot()
        ...
    except:
        self._closeDB(root)
	self._delDB()
	raise

which fails with an UnboundLocalError if the first line in the try
clause fails.  Fixed this by setting 'root = None' before each such
try clause, and adding a None check to _closeDB().  Also removed a
useless 'root = None' from the body of _closeDB().

Barry: I saw this in the saz 1.0c1 release.  Is it worth backporting?
Probably not given that we're not going to do a merge pre-1.0.