webdav.properties: warn about redirects to http.

I've submitted a feature request at #3736 to enable redirects to https, but I don't expect it to be implemented soon; therefore this pull request for a warning.

skel/share/defaults/webdav.properties

@@ -302,6 +302,10 @@ webdav.authz.allowed-paths = /
 #   HTTPS, a server certificate and a trust store need to be
 #   created. By default these are stored under /etc/grid-security/.
 #
+#   WARNING: when https is specified and redirects are enabled, 
+#   authentication will be done over https but files will be
+#   transferred over http.
+#
 (one-of?http|https)webdav.authn.protocol = http
 
 (immutable)webdav.authn.connector-for-http = PLAIN
@@ -677,4 +681,4 @@ webdav.authz.spnego.file=${dcache.paths.etc}/spnego.properties
 #   Non-JavaScript clients are unaffected by
 #   this property.
 #
-webdav.allowed.client.origins =
+webdav.allowed.client.origins =