Start a changelog for 0.4.5.1-alpha.

  o Minor bugfixes (logging):

    - When logging a rate-limited message about how many messages have been

      suppressed in the last N seconds, give an accurate value for N, rounded

      up to the nearest minute.  Previously we would report the size of the

      rate-limiting interval, regardless of when the messages started to

      occur.  Fixes bug 19431; bugfix on 0.2.2.16-alpha.

  o Minor bugfixes (self-testing):

    - When receiving an incoming circuit, only accept it as evidence that we

      are reachable if the declared address of its channel is the same

      address we think that we have.  Otherwise, it could be evidence that

      we're reachable on some other address. Fixes bug 20165; bugfix on

      0.1.0.1-rc.

  o Minor bugfixes (protover):

    - Consistently reject extra commas, instead of only rejecting leading commas.

      Fixes bug 27194; bugfix on 0.2.9.4-alpha.

  o Minor bugfixes (circuitpadding):

    - Add a per-circuit padding machine instance counter, so we can

      differentiate between shutdown requests for old machines on a circuit;

      Fixes bug 30992; bugfix on 0.4.1.1-alpha.

  o Minor bugfixes (circuitpadding):

    - Add the abilility to keep circuit padding machines if they match a set

      of circuit state or purposes. This allows us to have machines that start

      up under some conditions but don't shut down under others. We now

      use this mask to avoid starting up introduction circuit padding

      again after the machines have already completed. Fixes bug 32040;

      bugfix on 0.4.1.1-alpha.