title: /usr/local has correct permissions, but brew update still says it is not writable
body: <p>Here are the permissions to my <code>/usr/local</code> directory: <code>drwxr-xr-x</code>.</p>
  
  <p>I did <code>sudo chown -R $user /usr/local</code>, then did <code>brew update</code> again. It didn't work. I tried quitting terminal and opening a new session and trying again and I got the same thing. When I try <code>brew doctor</code> or <code>brew update</code>, it tells me that this directory is not writable. What do I do? What else do I need to be checking?</p>