lock pth file
remove fake deps
avoid duplicated entries in pth file
added documentation, patchlevel bump
resolved merge conflict
Trac #13201: patch setuptools to allow for parallel usage

Currently we have to force the spkgs that use setuptools to build
serially because setuptools does not do any file locking with
`easy_install.pth`. This is an inconvenience that has a fairly
straightforward fix.

URL: http://trac.sagemath.org/13201
Reported by: ohanar
Ticket author(s): Volker Braun
Reviewer(s): R. Andrew Ohana