title: how to exactly match using :class selector in watir-webdriver
body: <p>Regarding the backwards-incompatible change of Watir 0.5.x
  <a href="https://github.com/watir/watir-webdriver/issues/36" rel="nofollow">Finding elements by :class now matches partial class attributes.</a></p>
  
  <p>How do I get the old behavior? I.e. to match exact class name.</p>
  
  <p>It is breaking my code, in one case:</p>
  
  <pre class="lang-rb prettyprint-override"><code># expand all multiple records
   while  $browser.div(:class =&gt; "expander").exists?  
    $browser.div(:class =&gt; "expander").click
   end
  </code></pre>
  
  <p>because once <code>.click</code>ed, the <code>div</code>'s <strong>class</strong> becomes  <strong>"expander hasChildren"</strong> (and possibly other classes, depending on table row's color and content).   Is there a better way to write that code that expands all rows that are still collapsed?</p>