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/stripslash.c

@@ -0,0 +1,45 @@
+/* stripslash.c -- remove redundant trailing slashes from a file name
+
+   Copyright (C) 1990, 2001, 2003-2006, 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/>.  */
+
+#include <config.h>
+
+#include "dirname.h"
+
+/* Remove trailing slashes from FILE.  Return true if a trailing slash
+   was removed.  This is useful when using file name completion from a
+   shell that adds a "/" after directory names (such as tcsh and
+   bash), because on symlinks to directories, several system calls
+   have different semantics according to whether a trailing slash is
+   present.  */
+
+bool
+strip_trailing_slashes (char *file)
+{
+  char *base = last_component (file);
+  char *base_lim;
+  bool had_slash;
+
+  /* last_component returns "" for file system roots, but we need to turn
+     "///" into "/".  */
+  if (! *base)
+    base = file;
+  base_lim = base + base_len (base);
+  had_slash = (*base_lim != '\0');
+  *base_lim = '\0';
+  return had_slash;
+}