We need to set up an interpreteer copy which has 'persistent' already
installed, to prevent the on-demand eggs for 'persistent' and
'zope.interface' from screwing up the rest of the buildout.

Avoid relying on overflows w.r.t. sys.maxint.

Suppress warning under 'tox -e docs'

Fix them under Py3k.

Instead, OR it with METH_VARARGS.