(Re)fork any gist, including your own

readme.md

Want to fork your own gists? No fork button? No problem! Install this user script by clicking refork.user.js' "raw" link down below: ⇓

refork.user.js

// ==UserScript==
// @name           (Re)fork any gist, including your own
// @namespace      https://github.com/johan
// @version        2.0 - updated 2015-06-21
// @description    Adds a "fork" button to gists missing one at gist.github.com, so you can create multiple forks
// @match          https://gist.github.com/*
// @include        https://gist.github.com/*
// ==/UserScript==

if (/^\/[^\/]+\/\d+/.test(location.pathname) &&
    !document.querySelector('form[action$="/fork"]')) {
  var actions = document.querySelector('.gisthead .pagehead-actions')
    , auth = document.querySelector('input[name="authenticity_token"]').outerHTML
    , fork = document.createElement('li')
    , url = location.pathname + '/fork'
    ;
  fork.innerHTML = '<form accept-charset="UTF-8" action="'+ url + '" method="post"><div style="margin:0;padding:0;display:inline"><input name="utf8" type="hidden" value="✓">' + auth + '</div><button class="btn btn-sm" type="submit"><span class="octicon octicon-repo-forked"></span>Fork</button></form>';
  actions.appendChild(fork);
}

Thank you. I've already been cloning my gists using Sourcetree and actually I've been using local repo to manipulate / clean the gist history.
Anyway, forking own repo does not seem to be supported at all: "message": "You cannot fork your own gist."

community/community#14882

@RichardBronosky did you ever figure out what specifically makes a fork be indicated in the gist web interface?