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/allocator.h

@@ -0,0 +1,58 @@
+/* Memory allocators such as malloc+free.
+
+   Copyright (C) 2011-2017 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 Paul Eggert.  */
+
+#ifndef _GL_ALLOCATOR_H
+#define _GL_ALLOCATOR_H
+
+#include <stddef.h>
+
+/* An object describing a memory allocator family.  */
+
+struct allocator
+{
+  /* Do not use GCC attributes such as __attribute__ ((malloc)) with
+     the function types pointed at by these members, because these
+     attributes do not work with pointers to functions.  See
+     <http://lists.gnu.org/archive/html/bug-gnulib/2011-04/msg00007.html>.  */
+
+  /* Call ALLOCATE to allocate memory, like 'malloc'.  On failure ALLOCATE
+     should return NULL, though not necessarily set errno.  When given
+     a zero size it may return NULL even if successful.  */
+  void *(*allocate) (size_t);
+
+  /* If nonnull, call REALLOCATE to reallocate memory, like 'realloc'.
+     On failure REALLOCATE should return NULL, though not necessarily set
+     errno.  When given a zero size it may return NULL even if
+     successful.  */
+  void *(*reallocate) (void *, size_t);
+
+  /* Call FREE to free memory, like 'free'.  */
+  void (*free) (void *);
+
+  /* If nonnull, call DIE (SIZE) if MALLOC (SIZE) or REALLOC (...,
+     SIZE) fails.  DIE should not return.  SIZE should equal SIZE_MAX
+     if size_t overflow was detected while calculating sizes to be
+     passed to MALLOC or REALLOC.  */
+  void (*die) (size_t);
+};
+
+/* An allocator using the stdlib functions and a null DIE function.  */
+extern struct allocator const stdlib_allocator;
+
+#endif /* _GL_ALLOCATOR_H */