workaround a python bug

without this patch, "python ./setup.py install" produced the following
errors with python 2.7.3 on ubuntu 12.04.

Error in sys.exitfunc:
Traceback (most recent call last):
  File "/usr/lib/python2.7/atexit.py", line 24, in _run_exitfuncs
    func(*targs, **kargs)
  File "/usr/lib/python2.7/atexit.py", line 24, in _run_exitfuncs
    func(*targs, **kargs)
  File "/usr/lib/python2.7/multiprocessing/util.py", line 284, in _exit_function
    info('process shutting down')
TypeError: 'NoneType' object is not callable

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

setup.py

@@ -14,6 +14,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# a bug workaround.  http://bugs.python.org/issue15881
+try:
+    import multiprocessing
+except ImportError:
+    pass
+
 import setuptools
 import os