test_multiprocessing crashes on platforms that lack a working
sem_open(), despite it being turned off at compilation time by setting
HAVE_SEM_OPEN=0 in the Extension macros in setup.py

I think the multiprocessing module should disable the functionality
gracefully when it is missing from _multiprocessing.

Failure message:

test test_multiprocessing crashed -- <type 'exceptions.AttributeError'>:
'module' object has no attribute 'SemLock'
Traceback (most recent call last):
  File ".//Lib/test/regrtest.py", line 556, in runtest_inner
    indirect_test()
  File
"/usr/ports/lang/python/2.6/w-Python-2.6b3/Python-2.6b3/Lib/test/test_multiprocessing.py",
line 1758, in test_main
    ProcessesMixin.pool = multiprocessing.Pool(4)
  File
"/usr/ports/lang/python/2.6/w-Python-2.6b3/Python-2.6b3/Lib/multiprocessing/__init__.py",
line 226, in Pool
    return Pool(processes, initializer, initargs)
  File
"/usr/ports/lang/python/2.6/w-Python-2.6b3/Python-2.6b3/Lib/multiprocessing/pool.py",
line 84, in __init__
    self._setup_queues()
  File
"/usr/ports/lang/python/2.6/w-Python-2.6b3/Python-2.6b3/Lib/multiprocessing/pool.py",
line 130, in _setup_queues
    from .queues import SimpleQueue
  File
"/usr/ports/lang/python/2.6/w-Python-2.6b3/Python-2.6b3/Lib/multiprocessing/queues.py",
line 22, in <module>
    from multiprocessing.synchronize import Lock, BoundedSemaphore,
Semaphore, Condition
  File
"/usr/ports/lang/python/2.6/w-Python-2.6b3/Python-2.6b3/Lib/multiprocessing/synchronize.py",
line 29, in <module>
    SEM_VALUE_MAX = _multiprocessing.SemLock.SEM_VALUE_MAX
AttributeError: 'module' object has no attribute 'SemLock'
1 test failed:
    test_multiprocessing