title: Getting warning when generating sprites with compass / sass
body: <p>I have an issue with compass Im not able to find out.</p>
  
  <p>Every time I compile, when compass find a intruction like:</p>
  
  <pre><code>@import "base-icons/*.png";
  </code></pre>
  
  <p>Compass throw:</p>
  
  <pre><code>WARNING: Compass::SpriteImporter should define the #public_url method.
  </code></pre>
  
  <p>Actually, it compiles and everything is working fine. </p>
  
  <p>Unfortunately, I cannot find information about this issue, and I hate to see warnings on my console.</p>
  
  <p>Anyone know what could be happening ? How can I get rid of this ? Or which are the consequences of this message, what does it mean ?</p>
  
  <p>Thanks in advance !</p>