BLD: fix setuptools-specific easy_install issue.  Closes gh-3160.

An error is raised by setuptools when trying to write to /dev/null.  Was fixed
in distribute, but not in setuptools.

No multi-arch support with plain setuptools should be OK, because multi-arch is
Ubuntu specific (at least for now), and they ship distribute.
Merge pull request #3342 from rgommers/easyinstall-issue

BLD: fix setuptools-specific easy_install issue.  Closes gh-3160.