title: How can I see what branch another branch was forked from?
body: <p>My git repository has three branches, <code>devel</code>, <code>stable</code> and <code>customers/acme_patches</code>. A long time ago, <code>stable</code> was forked from <code>devel</code>, and all the bugfixing takes place in <code>stable</code>. Every now and then, <code>stable</code> is merged back into <code>devel</code>. <code>customers/acme_patches</code> is a branch with a few customer-specific patches. The branch wasn't merged into either of <code>devel</code> and <code>stable</code>.</p>
  
  <p>A bit of ASCII art to illustrate the scenario:</p>
  
  <pre>
              o---o---o          customers/acme_patches?
             /
    o---o---1---o---o---o        stable
   /     \           \
  o---o---o---2---o---o---o---o  devel
               \
                o---o---o        customers/acme_patches?
  </pre>
  
  <p>Now I wonder:</p>
  
  <p>What branch was <code>customers/acme_patches</code> forked from - <code>devel</code> or <code>stable</code>? I only know that it was forked off one of them in the past, but I don't know which. E.g. it might have been commit <code>1</code> or <code>2</code> in the above diagram.</p>
  
  <p>I've been playing around with <code>git log --oneline --graph</code> and <code>gitk</code> but since <code>customers/acme_patches</code> was forked a few hundred commits ago, it's hard to follow the lines being drawn.</p>
  
  <p>Is there maybe a quick command (a little script is fine, too) which can somehow follow the commits in <code>customers/acme_patches</code> backwards to find the first commit with two children (the fork point) and then determines whether that commit was done in <code>stable</code> or in <code>devel</code>?</p>
  
  <p>In the best case, I could just execute something like (excuse the prompt, I'm on Windows):</p>
  
  <pre><code>C:\src&gt; git fork-origin customers/acme_patches
  stable
  </code></pre>