case sensitive extras not handled for dist-info (wheel) installs

Originally reported by: qwcode (Bitbucket: qwcode, GitHub: qwcode)

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aiomas-0.3.0 has case sensitive extras

#!python

    extras_require={
        'MsgPack': ['msgpack-python>=0.4.4'],
        'MsgPackBlosc': ['blosc>=1.2.4', 'msgpack-python>=0.4.4'],
    },

after a pip sdist install, everything is ok

#!
pip install --no-use-wheel aiomas

#!python

>>> import pkg_resources
>>> d = pkg_resources.get_distribution('aiomas')
>>> d.requires(d.extras)
[Requirement.parse('arrow>=0.4.4'), Requirement.parse('blosc>=1.2.4'), Requirement.parse('msgpack-python>=0.4.4'), Requirement.parse('msgpack-python>=0.4.4')]

after a pip wheel install, everything is not ok

#!
pip install  aiomas

#!python

>>> import pkg_resources
>>> d = pkg_resources.get_distribution('aiomas')
>>> d.requires(d.extras)
[Requirement.parse('arrow>=0.4.4')]

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• Bitbucket: https://bitbucket.org/pypa/setuptools/issue/362