Use compat's StringIO. Should fix bitbucket #213

https://bitbucket.org/pypa/setuptools/issue/213/regression-setuptools-37-installation

--HG--
extra : source : 182f68beacf5e436609fb7d1064a18279cbbd24a
Bumped to 3.7.1 in preparation for next release.
Update changelog
Added tag 3.7.1 for changeset 9b422fc0b8b9
Bumped to 3.7.2 in preparation for next release.
Merge with 3.7.1
Bumped to 4.0.1 in preparation for next release.
Added tag 4.0.1 for changeset b14a51112acf
Bumped to 4.0.2 in preparation for next release.
Merge with 4.0.1