Discard the accumulated "heuristics" to guess from which branch the
result wants to be pulled from and make sure what the end user
specified is not second-guessed by "git request-pull", to avoid
mistakes.

* lt/request-pull:
  request-pull: documentation updates
  request-pull: resurrect "pretty refname" feature
  request-pull: test updates
  request-pull: pick up tag message as before
  request-pull: allow "local:remote" to specify names on both ends
  request-pull: more strictly match local/remote branches