Update references to the extension messaging APIs to point to the "runtime"

chrome/common/extensions/docs/templates/articles/whats_new.html

 <h1>What's New in Extensions?</h1>
 <!--  -->
 
 <p>
 This page lists the API and manifest changes
 made in recent releases.
 </p>
 
 <h2 id="22"> Google Chrome 22 </h2>
 
@@ skipping 97 matching lines @@
       $ref:tabs.insertCSS
       now accept a <code>runAt</code> parameter.</li>
   </ul>
 
 <h4> Changes to existing APIs </h4>
 
   <ul>
     <li>The <code>sendRequest()</code> method
       has been deprecated in favor of the
       <code>sendMessage()</code> method for both the
-      $ref:extension.sendMessage and
+      $ref:runtime.sendMessage and
       $ref:tabs.sendMessage.</li>
     <li>The <a href="external_extensions.html">external_extensions.json file</a>
       has been deprecated in favor of individual
       <code>&lt;extension-id&gt;.json</code> files.</li>
   </ul>
 
 <h2 id="19"> Google Chrome 19 </h2>
 
 <h4> New APIs </h4>
    <ul>
@@ skipping 494 matching lines @@
 <h4> Manifest changes </h4>
   <ul>
     <li>The <a href="manifest.html#geolocation">geolocation</a> permission
       gives an extension access to the user's physical location.
     <li><a href="match_patterns.html">Match patterns</a> can now select all
       schemes or all URLs.
     <li>Access to file:/// URLs no longer triggers the "access to your machine"
       security warning, but now requires user opt-in from the extensions
       management page.
   </ul>