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CLA is signed and now visible in my account.

cc @ncoghlan

Sorry for taking so long to review this @CuriousLearner.

I'm afraid I really don't like the notion of making pydoc natively aware of _sitebuiltins._Helper - that's two distinct cases of coupling a general purpose module shared across Python implementations to interpreter implementation details that aren't guaranteed to exist outside of CPython.

Added the sprint label, as this PR was submitted at the PyCon Pune 2017 core development sprint.