``PYTHONPATH`` directory with ``--multi-version``, unless an
``easy-install.pth`` file is already in use there.

(Bugfix merge from 0.7 trunk)

--HG--
branch : setuptools-0.6
extra : convert_revision : svn%3A6015fed2-1504-0410-9fe1-9d1591cc4771/sandbox/branches/setuptools-0.6%4046143