This is added for compatibility with zope.pagetemplate 4.0.0.
The argument is ignored.
See LP #732972.

This merges r129010 from branch 2.13.

...
  File "...\eggs\zope2-2.13.15-py2.7.egg\Zope2\Startup\run.py", line 72, in make_wsgi_app
    starter.prepare()
  File "...\eggs\zope2-2.13.15-py2.7.egg\Zope2\Startup\__init__.py", line 83, in prepare
    self.makeLockFile()
  File "...\eggs\zope2-2.13.15-py2.7.egg\Zope2\Startup\__init__.py", line 278, in makeLockFile
    os.unlink(lock_filename)
WindowsError: [Error 32] The process cannot access the file because it is being used by another process: '.../var/client1/client1.lock'

To be sure that "in" is supported
I'd have to check for multiple possible
builtin attributes. Instead I do a try 
except.

- related cleanup