Implemented __reduce__ in a way compatible with normal functions, works fine now.

Released as part of 0.3.22.1 hotfix release

Test case by Adrià Cereto Massagué that shows this issue also affects 
multiprocessing module.

The "test_copy" case from CPython2.6 exhibits the following traceback:

  File "/usr/lib/python2.6/copy_reg.py", line 93, in __newobj__
    return cls.__new__(cls, *args)
TypeError: object.__new__(compiled_function) is not safe, use 
compiled_function.__new__()

Need to investigate, why it considers the "__new__" to be unsafe. Might not be 
necessary.