Basic inter-process locks for Python 3

 The zc.lockfile package provides a basic portable implementation of
 interprocess locks using lock files. The purpose if not specifically to lock
 files, but to simply provide locks with an implementation based on
 file-locking primitives. Of course, these locks could be used to mediate
 access to *other* files. For example, the ZODB file storage implementation
 uses file locks to mediate access to file-storage database files. The database
 files and lock file files are separate files.