title: XPath expression doesn't match "%20" on iOS
body: <p>I'm having a problem while looking for a string with <code>%20</code> in a xml using xpath.
  I'm trying to match this string this:</p>
  
  <pre><code> &lt;navMap&gt;
      ...
      &lt;navPoint id="navpoint-2" playOrder="3"&gt;
          &lt;navLabel&gt;
              &lt;text&gt;Title&lt;/text&gt;
          &lt;/navLabel&gt;
          &lt;content src="My%20book%20OK.xhtml"/&gt;
      &lt;/navPoint&gt;
      ...
  &lt;/navMap&gt;
  </code></pre>
  
  <p>This is my query:</p>
  
  <pre><code>//ncx:content[@src='My%20book%20OK.xhtml']/../ncx:navLabel/ncx:text
  </code></pre>
  
  <p>It works for elements with <code>@src</code> not containing <code>%20</code>, but not for the one given above.</p>