RF: delete implemention of itertools.permutations
RF: delete implemention of itertools.permutations

Present in Python 2.6 and above.

alexis-roche/nipy,alexis-roche/nipy,alexis-roche/nireg,nipy/nireg,alexis-roche/nipy,alexis-roche/nipy,alexis-roche/nireg,nipy/nireg