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/pipe.c

@@ -0,0 +1,50 @@
+/* Create a pipe.
+   Copyright (C) 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, 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 <config.h>
+
+/* Specification.  */
+#include <unistd.h>
+
+#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
+/* Native Windows API.  */
+
+/* Get _pipe().  */
+# include <io.h>
+
+/* Get _O_BINARY.  */
+# include <fcntl.h>
+
+int
+pipe (int fd[2])
+{
+  /* Mingw changes fd to {-1,-1} on failure, but this violates
+     http://austingroupbugs.net/view.php?id=467 */
+  int tmp[2];
+  int result = _pipe (tmp, 4096, _O_BINARY);
+  if (!result)
+    {
+      fd[0] = tmp[0];
+      fd[1] = tmp[1];
+    }
+  return result;
+}
+
+#else
+
+# error "This platform lacks a pipe function, and Gnulib doesn't provide a replacement. This is a bug in Gnulib."
+
+#endif