* lisp/emacs-lisp/package.el (package-installed-p): Warn if not ready.

Fixes: debbugs:12721

lisp/ChangeLog

+2012-10-25  Stefan Monnier  <monnier@iro.umontreal.ca>
+
+	* emacs-lisp/package.el (package-installed-p): Warn if not ready
+	(bug#12721).
+
 2012-10-25  Glenn Morris  <rgm@gnu.org>
 
 	* emacs-lisp/cl-macs.el (cl-progv): Doc fix.

lisp/emacs-lisp/package.el

@@ -728,6 +728,7 @@ It will move point to somewhere in the headers."
 (defun package-installed-p (package &optional min-version)
   "Return true if PACKAGE, of MIN-VERSION or newer, is installed.
 MIN-VERSION should be a version list."
+  (unless package--initialized (error "package.el is not yet initialized!"))
   (let ((pkg-desc (assq package package-alist)))
     (if pkg-desc
 	(version-list-<= min-version