o Minor bugfixes (vanguards):
    - Allow the last hop in a vanguard circuit to be the same as our first,
      to prevent the adversary from influencing guard node choice by choice
      of last hop. Also prevent the creation of A - B - A paths, or A - A
      paths, which are forbidden by relays. Fixes bug 25870; bugfix on
      0.3.3.1-alpha.