- Fixed the pathing used when tests run; for sqla_nose.py and py.test,

- Fixed the pathing used when tests run; for sqla_nose.py and py.test,
the "./lib" prefix is again inserted at the head of sys.path but
only if sys.flags.no_user_site isn't set; this makes it act just
like the way Python puts "." in the current path by default.
For tox, we are setting the PYTHONNOUSERSITE flag now.
fixes #3356