Changes file.

  o Major features (Circuit padding):

    - Onion service clients will now add padding cells to the initial portions

      of their INTRODUCE and RENDEZVOUS circuits, to make those circuits'

      traffic patterns look more like general purpose Exit traffic. The

      overhead for this is 2 extra cells in each direction for RENDEZVOUS

      circuits, and 1 extra upstream cell and 10 downstream cells for INTRODUCE

      circuits. This will only be enabled if the circuit's middle node supports

      this feature, too. (Clients may specify fixed middle nodes with the MiddleNodes

      torrc directive, and may force-disable this feature with the CircuitPadding

      torrc directive). Closes ticket 28634.