tor/changes/bug2756

  o Minor bugfixes (spec conformance, performance):
    - We now ask the other side of a stream (the client or the exit)
      for more data on that stream when the amount of queued data on
      that stream dips low enough.  Previously, we wouldn't ask the
      other side for more data until either it sent us more data
      (which it wasn't supposed to do if it had exhausted its
      window!) or until we had completely flushed all our queued
      data.  Fixing this should improve throughput.  Fixes bug 2756;
      bugfix on the earliest released versions of Tor (svn commit
      r152).