Ehm.. completly broken url in prev message.. Revision 65016, "Apply
Amaury's patch to multiprocessing for issue 3125, removes the copy_reg
and replaces it with ForkingPickler.register(), which should resolve the
conflict with the global registry/ctypes" is what I'm refering to.
Without this patch, the reducers/rebuilders are properly registered in
the pickler that connection.h (srsly, code in header files?) later uses.