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/strftime.h

@@ -0,0 +1,33 @@
+/* declarations for strftime.c
+
+   Copyright (C) 2002, 2004, 2008-2017 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 of the License, 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/>.  */
+
+#include <time.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Just like strftime, but with two more arguments:
+   POSIX requires that strftime use the local timezone information.
+   Use the timezone __TZ instead.  Use __NS as the number of
+   nanoseconds in the %N directive.  */
+size_t nstrftime (char *, size_t, char const *, struct tm const *,
+                  timezone_t __tz, int __ns);
+
+#ifdef __cplusplus
+}
+#endif