D7: editor multi-cursor support

Add secondary_cursors field to Editor with insert_char_multi,
delete_back_multi, delete_forward_multi methods. Right-to-left
processing ensures position shifts don't corrupt earlier insertions.

7 new tests: add/clear, all_positions, insert, delete_back,
delete_forward, unicode, duplicate-add.

local/recipes/tools/diffutils/source/lib/time_r.c

@@ -0,0 +1,44 @@
+/* Reentrant time functions like localtime_r.
+
+   Copyright (C) 2003, 2006-2007, 2010-2017 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License along
+   with this program; if not, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert.  */
+
+#include <config.h>
+
+#include <time.h>
+
+static struct tm *
+copy_tm_result (struct tm *dest, struct tm const *src)
+{
+  if (! src)
+    return 0;
+  *dest = *src;
+  return dest;
+}
+
+
+struct tm *
+gmtime_r (time_t const * restrict t, struct tm * restrict tp)
+{
+  return copy_tm_result (tp, gmtime (t));
+}
+
+struct tm *
+localtime_r (time_t const * restrict t, struct tm * restrict tp)
+{
+  return copy_tm_result (tp, localtime (t));
+}