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/m4/strftime.m4

@@ -0,0 +1,22 @@
+# serial 34
+
+# Copyright (C) 1996-1997, 1999-2007, 2009-2017 Free Software Foundation, Inc.
+#
+# This file is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+# Written by Jim Meyering and Paul Eggert.
+
+AC_DEFUN([gl_FUNC_GNU_STRFTIME],
+[
+ # This defines (or not) HAVE_TZNAME and HAVE_TM_ZONE.
+ AC_REQUIRE([AC_STRUCT_TIMEZONE])
+
+ AC_REQUIRE([gl_TM_GMTOFF])
+
+ AC_CHECK_FUNCS_ONCE([tzset])
+
+ AC_DEFINE([my_strftime], [nstrftime],
+   [Define to the name of the strftime replacement function.])
+])