Support namedtuple's getitem

[pylint-bot]

Originally reported by: Claudiu Popa (BitBucket: PCManticore, GitHub: @PCManticore?)

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We should detect namedtuple's indexing, as it is the case for this example:

#!python

from collections import namedtuple
f = namedtuple('a', 'a b')
c = f(1, 2)
print(c[0].lala)

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• Bitbucket: https://bitbucket.org/logilab/astroid/issue/182