o Minor bugfixes (correctness):
    - Fix a bad memory handling bug that would occur if we had queued
      a cell on a channel's incoming queue. Fortunately, we can't actually
      queue a cell like that as our code is constructed today, but it's best
      to avoid this kind of error, even if there isn't any code that triggers
      it today. Fixes bug 18570; bugfix on 0.2.4.4-alpha.