bug#15519: 24.3; secrets.el `secrets-create-collection' is broken (fix included)

[Nicolas Petton]

In secrets.el, secrets-create-collection is broken (the DBus message
signature is wrong and the collection label is not the right one).

Here's a fixed version of the function:

(defun secrets-create-collection (collection)
  "Create collection labeled COLLECTION if it doesn't exist.
Return the D-Bus object path for collection."
  (let ((collection-path (secrets-collection-path collection)))
    ;; Create the collection.
    (when (secrets-empty-path collection-path)
      (setq collection-path
            (secrets-prompt
             (cadr
              ;; "CreateCollection" returns the prompt path as second arg.
              (dbus-call-method
               :session secrets-service secrets-path
               secrets-interface-service "CreateCollection"
               `(:array 
                 (:dict-entry
"org.freedesktop.Secret.Collection.Label" (:variant ,collection)))
               "")))))
    ;; Return object path of the collection.
    collection-path))