changes file for bug11743

  o Major security fixes (directory authorities):

    - Directory authorities now include a digest of each relay's

      identity key as a part of its microdescriptor.

      This is a workaround for bug #11743, where Tor clients do not

      support receiving multiple microdescriptors with the same SHA256

      digest in the same consensus. When clients receive a consensus

      like this, they only use one of the relays. Without this fix, a

      hostile relay could selectively disable client use of target

      relays by constucting a router descriptor with a different

      identity and the same microdescriptor parameters and getting the

      authorities to list it in a microdescriptor consensus. This fix

      prevents an attacker from causing a microdescriptor collision,

      because the router's identity is not forgeable.