o Minor bugfixes (onion services):
    - On an intro point for a version 3 onion service, we do not close
      an introduction circuit on an NACK. This lets the client decide
      whether to reuse the circuit or discard it. Previously, we closed
      intro circuits on NACKs. Fixes bug 27841; bugfix on 0.3.2.1-alpha.
      Patch by Neel Chaunan