Merged [2628] from lars.eggert@nokia.com:

Fix for ietf-tools#467. 
 * History tab: Avoid HTTP/HTTPS warning for the diff tool form submission.
 - Legacy-Id: 2638
Note: SVN reference [2628] has been migrated to Git commit f7b1047

Author: levkowetz

ietf/templates/idrfc/doc_diffs.html

@@ -34,7 +34,7 @@
 
 <div class="ietf-box diffTool">
 <h2 style="margin-top:0;margin-bottom:4px;">Diffs</h2>
-<form action="http://tools.ietf.org/rfcdiff" method="get" target="_blank" style="margin:0;">
+<form action="http{% if request.is_secure %}s{% endif %}://tools.ietf.org/rfcdiff" method="get" target="_blank" style="margin:0;">
 <table>
 <tr><td>
 <label>From:</label> <select name="url1">