security format patch

[Ivailo]

Attached a patch that fixes a test build failure caused by use of
-Wformat -Werror=format-security in build flags. Take the credits,
I don't want medals and such.

Cheers!

--- gnulib-tests/test-xvasprintf.c.new	2013-12-02 20:39:45.327821760 +0000
+++ gnulib-tests/test-xvasprintf.c	2013-03-22 04:20:50.000000000 +0000
@@ -95,7 +95,7 @@
   {
     /* Silence gcc warning about zero-length format string.  */
     const char *empty = "";
-    result = xasprintf (empty);
+    result = xasprintf ("%s", empty);
     ASSERT (result != NULL);
     ASSERT (strcmp (result, "") == 0);
     free (result);