Use correct protocol in shared links (https/http)

lms/templates/courseware/course_about_sidebar_header.html

@@ -16,6 +16,7 @@ from django.conf import settings
     ##       want here (and on this whole page, really).
       <%
         site_domain = static.get_value('site_domain', settings.SITE_NAME)
+        site_protocol = 'https' if settings.HTTPS == 'on' else 'http'
         platform_name = static.get_platform_name()
 
         ## Translators: This text will be automatically posted to the student's
@@ -24,7 +25,8 @@ from django.conf import settings
             number=course.number,
             title=course.display_name_with_default_escaped,
             account=static.get_value('course_about_twitter_account', settings.PLATFORM_TWITTER_ACCOUNT),
-            url=u"http://{domain}{path}".format(
+            url=u"{protocol}://{domain}{path}".format(
+                protocol=site_protocol,
                 domain=site_domain,
                 path=urllib.quote_plus(
                     reverse('about_course', args=[course.id.to_deprecated_string()])
@@ -41,7 +43,8 @@ from django.conf import settings
                 number=course.number,
                 title=course.display_name_with_default_escaped,
                 platform=platform_name,
-                url=u"http://{domain}{path}".format(
+                url=u"{protocol}://{domain}{path}".format(
+                    protocol=site_protocol,
                     domain=site_domain,
                     path=urllib.quote_plus(
                         reverse('about_course', args=[course.id.to_deprecated_string()]),