This fixes errors like:
- ConnectorException: makeListeningConnection on ('127.0.0.1', 33157) failed: 98:Address already in use
  Error executing './neomaster ...
- "error: [Errno 22] Invalid argument" in __allocatePort

A system-wide lock is used to prevent conflicts when several NEO test suites are
run simultaneously.

However, errors could still happen if other software tries to allocate ports.
Allocated ports are kept open as long as possible to minimize the probability
that it happens: they are closed just before spawning subprocesses.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2665 71dcc9de-d417-0410-9af5-da40c76e7ee4