Fix some typos, broken links and other issues in extension docs

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

 <h1>Frequently Asked Questions</h1>
 
 
 <!--  -->
 
 <p>
 If you don't find an answer to your question here,
 try the
 <a href="http://code.google.com/chrome/webstore/faq.html">Chrome Web Store FAQ</a>, the
 <a href="http://stackoverflow.com/questions/tagged/google-chrome-extension">[google-chrome-extension] tag on Stack Overflow</a>, the
@@ skipping 59 matching lines @@
   extensions, you already have everything you need to start writing an
   extension of your own.
   You can start by turning on Developer mode.
   </p>
 
   <p>
   Click the Chrome menu icon
   <img src="{{static}}/images/hotdogmenu.png" height="29" width="29" alt=""
     class="nomargin" />
   and select <b>Extensions</b> from the <b>Tools</b> menu.
-  If there's a "+" next to "Developer mode",
-  click the "+" so it turns into a "-".
+  Ensure that the "Developer mode" checkbox in the top right-hand corner
+  is checked.
   Now you can reload extensions,
   load an unpacked directory of files as if it were a packaged extension,
   and more. For a complete tutorial, see
   <a href="http://code.google.com/chrome/extensions/getstarted.html">Getting Started</a>.
 </p>
 
 <h3 id="faq-gen-02">What technologies are used to write extensions for Chrome?</h3>
 <p>
   Extensions are written using the same standard web
   technologies that developers use to create websites. HTML is used as a
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 <p>
   Yes, extensions may pass messages to other extensions. See the
   <a href="messaging.html#external">message passing documentation</a>
   for more information.
 </p>
 
 <h3 id="faq-dev-13">Can extensions use Google Analytics?</h3>
 <p>
   Yes, since extensions are built just like websites, they can use
   <a href="http://www.google.com/analytics/">Google Analytics</a> to track
-  usage.  However, we strongly advise you to modify the tracking code to pull
+  usage.  However, you have to modify the tracking code to pull

[Mike West, 2013/02/11 08:21:53]

Please change "have" to "must" for clarity.

[方觉(Fang Jue), 2013/02/11 11:37:54]

Done.

   an HTTPS version of the Google Analytics library.  See
   <a href="tut_analytics.html">this tutorial</a> for more information on doing
   this.
 </p>
 
 <h3 id="faq-dev-15">Can extensions modify chrome:// URLs?</h3>
 <p>
   No. The extensions APIs have been designed to minimize backwards
   compatibility issues that can arise when new versions of the browser are
   pushed. Allowing content scripts on <code>chrome://</code>
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     <a href="http://groups.google.com/a/chromium.org/group/chromium-extensions/topics">
     discussion group</a> with a link back to your request.
   </li>
   <li>
     If you originally reported your request on the discussion group and were
     directed to this FAQ entry, reply to your original thread with a link
     to the ticket you starred or opened.  This will make it easier for others
     with the same request to find the correct ticket.
   </li>
 </ol>