title: [libpng]could not link symlink include/libpng16/png.h
body: <p>When I install imageMagick,it told me must link <code>libpng</code> before install imageMagick.</p>
  
  <p>Then I link the <code>libpng</code>,it occur this issue</p>
  
  <blockquote>
    <blockquote>
      <p>brew link libpng
      Linking /usr/local/Cellar/libpng/1.6.17...
      Error: Could not symlink include/libpng16/png.h
      Target /usr/local/include/libpng16/png.h
      already exists. You may want to remove it:
        rm '/usr/local/include/libpng16/png.h'</p>
    </blockquote>
  </blockquote>
  
  <p>To force the link and overwrite all conflicting files:</p>
  
  <pre><code>brew link --overwrite libpng
  </code></pre>
  
  <p>To list all files that would be deleted:</p>
  
  <pre><code>brew link --overwrite --dry-run libpng
  </code></pre>