new-calendar-page: add support for webcal:// links

Turns out, all we have to do is rewrite the URL to https://. I'm
surprised this works, but I don't see any problems with it. I tested
subscribing to webcal://www.gnome.org/start/unstable/schedule.ics.

See also: #481

src/gui/calendar-management/gcal-new-calendar-page.c

@@ -356,6 +356,16 @@ validate_url_cb (gpointer data)
 
   if (uri != NULL && SOUP_URI_IS_VALID (uri))
     {
+      /* "Support" webcal:// links by converting them to https://. This works
+       * because WebDAV is an extension of HTTP, so we can treat it as normal
+       * HTTP.
+       *
+       * Note we don't allow hidden use of http://, since we want to protect the
+       * user from accidentally leaking calendars in the clear. Only https://.
+       */
+      if (strcmp (uri->scheme, "webcal") == 0)
+        soup_uri_set_scheme (uri, SOUP_URI_SCHEME_HTTPS);
+
       discover_sources (self);
     }
   else