Minor fix to package-archive-contents recalculation.

lisp/emacs-lisp/package.el (package-read-all-archive-contents): Reset
package-archive-contents to nil before re-reading.

lisp/ChangeLog

+2010-11-10  Chong Yidong  <cyd@stupidchicken.com>
+
+	* emacs-lisp/package.el (package-read-all-archive-contents): Reset
+	package-archive-contents to nil before re-reading.
+
 2010-11-10  Brandon Craig Rhodes <brandon@rhodesmill.org>
 
 	* textmodes/flyspell.el (flyspell-word): Do not re-check words

lisp/emacs-lisp/package.el

@@ -753,6 +753,7 @@ Will throw an error if the archive version is too new."
 (defun package-read-all-archive-contents ()
   "Re-read `archive-contents', if it exists.
 If successful, set `package-archive-contents'."
+  (setq package-archive-contents nil)
   (dolist (archive package-archives)
     (package-read-archive-contents (car archive))))