Bugfix for `org-publish-get-files'.

`plist-get' was called with the wrong argument, thus causing an
error in old Emacsen where `plist-get' was not safe.

org-publish.el

@@ -381,7 +381,7 @@ If NO-EXCLUSION is non-nil, don't exclude files."
     ;; add all projects
     (mapc
      (lambda(p)
-       (let* ((exclude (plist-get p :exclude))
+       (let* ((exclude (plist-get (cdr p) :exclude))
 	      (files (org-publish-get-base-files p exclude)))
 	 ;; add all files from this project
 	 (mapc (lambda(f)