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/unused-parameter.h

@@ -0,0 +1,36 @@
+/* A C macro for declaring that specific function parameters are not used.
+   Copyright (C) 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/>.  */
+
+/* _GL_UNUSED_PARAMETER is a marker that can be appended to function parameter
+   declarations for parameters that are not used.  This helps to reduce
+   warnings, such as from GCC -Wunused-parameter.  The syntax is as follows:
+       type param _GL_UNUSED_PARAMETER
+   or more generally
+       param_decl _GL_UNUSED_PARAMETER
+   For example:
+       int param _GL_UNUSED_PARAMETER
+       int *(*param)(void) _GL_UNUSED_PARAMETER
+   Other possible, but obscure and discouraged syntaxes:
+       int _GL_UNUSED_PARAMETER *(*param)(void)
+       _GL_UNUSED_PARAMETER int *(*param)(void)
+ */
+#ifndef _GL_UNUSED_PARAMETER
+# if __GNUC__ >= 3 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 7)
+#  define _GL_UNUSED_PARAMETER __attribute__ ((__unused__))
+# else
+#  define _GL_UNUSED_PARAMETER
+# endif
+#endif