o Major bugfixes:

    - Don't launch a useless circuit after failing to use one of a
      hidden service's introduction points.  Previously, we would
      launch a new introduction circuit, but not set the hidden
      service which that circuit was intended to connect to, so it
      would never actually be used.  A different piece of code would
      then create a new introduction circuit correctly, so this bug
      was harmless until it caused an assertion in the client-side
      part of the #3825 fix to fail.  Bug reported by katmagic and
      found by Sebastian Hahn.  Bugfix on 0.2.1.13-alpha; fixes bug
      4212.