o Minor bugfixes:

    - Avoid strange behavior if two threads hit failed asswertions
      at the same time and both try to log backtraces at
      once. (Previously, if this had happened, both threads would
      have stored their intermediate results in the same buffer, and
      generated junk outputs.) Reported by "cypherpunks". Fixes bug
      11048; bugfix on 0.2.5.2-alpha.