tor/changes/1863_bwhist

  o Minor features
    - Servers now save observed maximum bandwidth throughput rates
      to their state file (along with total usage, which was already
      saved) so that they can determine their correct estimated
      bandwidth on restart.  Resolves bug 1863, where Tor servers
      would reset their estimated bandwidth to 0 after restarting.

  o Minor bugfixes
    - Fix a bug in banwidth history state parsing that could have been
      triggered if a future version of Tor ever changed the timing
      granularity at which bandwidth history is measured.  Bugfix on
      Tor 0.1.1.11-alpha.
    - Correctly clear out dir_read/dir_write history when there is an
      error parsing any bw history value from the state file. Bugfix on
      Tor 0.2.2.15-alpha.