python3 compatible next() for generator

[toliwaga]

replaced this
self._shape = self.iter_nodes(self.root.data,'CArray').next().shape
with this

            # jwd: generator has no next funtion in python 3 
            # next() function supported in both in python 2.6+ and python 3
            self._shape = next(self.iter_nodes(self.root.data,'CArray')).shape

Misspelled 'function' - sorry!

[bstabler]

#3