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

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

Index: chrome/common/extensions/docs/templates/articles/external_extensions.html
===================================================================
--- chrome/common/extensions/docs/templates/articles/external_extensions.html	(revision 181647)
+++ chrome/common/extensions/docs/templates/articles/external_extensions.html	(working copy)
@@ -38,7 +38,7 @@
 Both ways support installing an extension from a <code>.crx</code> extension
 file on the user's computer.  The preferences JSON file also supports installing
 an extension hosted at an
-<a href="autoupdate.html#H2-1">update URL</a>.
+<a href="autoupdate.html#update_url">update URL</a>.
 See <a href="hosting.html">hosting</a> for details on hosting an extension.
 </p>
 
@@ -51,7 +51,7 @@
 </p>
 <p>
 If you wish to install from an
- <a href="autoupdate.html#H2-1">update URL</a>, ensure that the extension
+ <a href="autoupdate.html#update_url">update URL</a>, ensure that the extension
 is properly <a href="hosting.html">hosted</a>.
 </p>
 
@@ -255,7 +255,7 @@
 <p>Yes, if you use a <a href="#preferences">preferences JSON</a> file. The
 extension must be hosted as explained in <a href="hosting.html">hosting</a>.
 Use the "external_update_url" property to point to an
-<a href="autoupdate.html#H2-2">update manifest</a> that has the URL for your
+<a href="autoupdate.html#update_manifest">update manifest</a> that has the URL for your
 extension.</p>
 
 <br>
@@ -311,4 +311,4 @@
 your extension through the UI,
 you can remove the blacklist tag
 by installing the extension normally
-through the UI, and then uninstalling it. </p>
+through the UI, and then uninstalling it. </p>