Fix bug#16161: CHECK_LIST_CONS fails on nil

* src/gnutls.c (Fgnutls_boot): Use `Flistp' instead of
`CHECK_LIST_CONS`.

src/ChangeLog

+2013-12-16  Teodor Zlatanov  <tzz@lifelogs.com>
+
+	* gnutls.c (Fgnutls_boot): Use `Flistp' instead of
+	`CHECK_LIST_CONS`.
+
 2013-12-16  Martin Rudalics  <rudalics@gmx.at>
 
 	* w32term.c (w32_enable_frame_resize_hack): Default to 1.

src/gnutls.c

@@ -825,7 +825,8 @@ one trustfile (usually a CA bundle).  */)
   verify_error          = Fplist_get (proplist, QCgnutls_bootprop_verify_error);
   prime_bits            = Fplist_get (proplist, QCgnutls_bootprop_min_prime_bits);
 
-  CHECK_LIST_CONS (verify_error, verify_error);
+  if (!Flistp (verify_error))
+    error ("gnutls-boot: invalid :verify_error parameter (not a list)");
 
   if (!STRINGP (hostname))
     error ("gnutls-boot: invalid :hostname parameter (not a string)");