keyring: Don't replace an already running prompter

* Prompters have state, and cancelling an already prompter will
   cause prompts that are in progress to fail.
 * In addition allow replacement of our shell prompter for debugging
   purposes.

https://bugzilla.gnome.org/show_bug.cgi?id=695485

js/ui/components/keyring.js

@@ -222,7 +222,7 @@ const KeyringPrompter = new Lang.Class({
     enable: function() {
         this._prompter.register(Gio.DBus.session);
         this._dbusId = Gio.DBus.session.own_name('org.gnome.keyring.SystemPrompter',
-                                                 Gio.BusNameOwnerFlags.REPLACE, null, null);
+                                                 Gio.BusNameOwnerFlags.ALLOW_REPLACEMENT, null, null);
     },
 
     disable: function() {