tor/changes/bug1937

  o Major bugfixes
    - When receiving a circuit-level SENDME for a blocked circuit, try
      to package cells fairly from all the streams that had previously
      been blocked on that circuit.  Previously, we had started with
      the oldest stream, and allowed each stream to potentially
      exhaust the circuit's package window.  This gave older streams
      on any given circuit priority over newer ones.  Fixes bug 1937.
      Detected by Camilo Viecco.  This bug was introduced before the
      first Tor release, in svn commit r152: it is the new winner of
      the longest-lived bug prize.