def previous_rev(self, rev, path=''):
        # FIXME optimize for non-scoped
        rev = self.normalize_rev(rev)
        return self._previous_rev(rev, path)
Return revision immediately preceeding `rev`, eventually below
dataset/ETHPy150Open edgewall/trac/tracopt/versioncontrol/svn/svn_fs.py/SubversionRepository.previous_rev