title: $(element).outerWidth(true) reports differently based on theme?
body: <p>I have a jQuery script, this sets an element's width to 50% via the normal CSS width attribute. </p>
  
  <p>If I then output the <code>outerWidth(true)</code> of that element to get the exact pixel value, it sometimes does not correspond to <code>$(window).width()/2</code> - this is based on the theme that the site has. Unfortunately I cannot bring a demo for this behavior online.</p>
  
  <p>Is there any specific CSS attribute that might cause such a difference? </p>
  
  <p>The problem is that the <code>outerWidth()</code> is reporting for example, <code>564px</code>, but when I check in Safari inspector, it says <code>580</code>. So the return of that function is incorrect and I'd like to be able to know what is the cause.</p>
  
  <p>Demo: </p>
  
  <p><a href="http://users.telenet.be/prullen/this/" rel="nofollow">http://users.telenet.be/prullen/this/</a></p>
  
  <p><a href="http://users.telenet.be/prullen/that/" rel="nofollow">http://users.telenet.be/prullen/that/</a></p>
  
  <p>The content (gray area when you click on the red tab) is supposed to be hidden on load via a negative margin, but due to the (incorrect?) return of jquery, it is not in one of these themes (showing slightly).</p>
  
  <p>console.log calls are : </p>
  
  <pre><code>        console.log('window width / 2 = ' + $(window).width()/2);
          console.log('doc width /2  = ' + $(document).width()/2);
  
          console.log('width = ' + defaults.boxWidth);
          console.log('width = ' + $slider.css('width'));
          console.log('width = ' + $slider.width());
          console.log('width = ' + $slider.outerWidth());
          console.log('width = ' + $slider.outerWidth(true));
  </code></pre>