Raised version number to 0.3.1

Define macro ATTRIBUTE_UNUSED.

@@ -17,7 +17,7 @@
 # Foundation, Inc.
 # 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 
-AC_INIT([GNU Mailutils], [0.3], [bug-mailutils@gnu.org], [mailutils])
+AC_INIT([GNU Mailutils], [0.3.1], [bug-mailutils@gnu.org], [mailutils])
 AC_CONFIG_SRCDIR([mailbox/mailbox.c])
 AC_CONFIG_AUX_DIR([scripts])
 AC_CANONICAL_TARGET([])
@@ -634,6 +634,18 @@ if test "$EMACS" != "no"; then
 fi
 AC_SUBST(lisp_LISP)
 
+dnl Define ATTRIBUTE_UNUSED macro
+dnl
+AH_BOTTOM([
+#if __GNUC__ < 2 || (__GNUC__ == 2 && __GNUC_MINOR__ < 7)
+#  define __attribute__(x)
+#endif
+
+#ifndef ATTRIBUTE_UNUSED
+# define ATTRIBUTE_UNUSED __attribute__ ((__unused__))
+#endif
+])
+
 dnl Make sysconfdir available to the application
 dnl This must be done LAST, since CPPFLAGS is passed by configure
 dnl to build tests, but this relies on being run in make to