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/gnulib-tests/test-sys_time.c

@@ -0,0 +1,34 @@
+/* Test of <sys/time.h> substitute.
+   Copyright (C) 2007, 2009-2017 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/>.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2007.  */
+
+#include <config.h>
+
+#include <sys/time.h>
+
+/* Check that the 'struct timeval' type is defined.  */
+struct timeval a;
+
+/* Check that a.tv_sec is wide enough to hold a time_t, ignoring
+   signedness issues.  */
+typedef int verify_tv_sec_type[sizeof (time_t) <= sizeof (a.tv_sec) ? 1 : -1];
+
+int
+main (void)
+{
+  return 0;
+}