tor/changes/fallbacks-201612

  o Minor features (fallback directories):
    - Select 200 fallback directories for each release.
      Closes ticket 20881.
    - Provide bandwidth and consensus weight for each candidate fallback in
      updateFallbackDirs.py.
      Closes ticket 20878.
    - Require fallback directories to have the same address and port for
      6 months. (We expect to regenerate the fallback list each major Tor
      release.) Relays whose OnionOO stability timer is reset on restart by
      bug 18050 should upgrade to Tor 0.2.8.7 or later, which has a fix for
      this issue.
      Closes ticket 20880; removes short-term fix in e220214 in
      tor-0.2.8.2-alpha.
    - Make it easier to change the output sort order of fallbacks.
      Closes ticket 20822.
    - Exclude relays affected by 20499 from the fallback list. Exclude known
      affected versions, and any relay that delivers a stale consensus.
      Closes ticket 20539.
  o Minor bugfix (fallback directories):
    - Stop failing when OUTPUT_COMMENTS is True in updateFallbackDirs.py.
      Closes ticket 20877; bugfix on commit 9998343 in tor-0.2.8.3-alpha.