I believe this is a Linux-specific problem relating to chroot jails 
missing the /dev/shm filesystem. 

I am suggesting we skip the test for now if /dev/shm does not exist, 
via:

if (sys.platform.startswith("linux"):
    if not os.path.exists("/dev/shm"):
        raise TestSkipped("Missing required /dev/shm device on Linux!")

at the top of test_multiprocessing.py

Anyone see a problem with this?