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/m4/builtin-expect.m4

@@ -0,0 +1,49 @@
+dnl Check for __builtin_expect.
+
+dnl Copyright 2016-2017 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+dnl Written by Paul Eggert.
+
+AC_DEFUN([gl___BUILTIN_EXPECT],
+[
+  AC_CACHE_CHECK([for __builtin_expect],
+    [gl_cv___builtin_expect],
+    [AC_LINK_IFELSE(
+       [AC_LANG_SOURCE([[
+         int
+         main (int argc, char **argv)
+         {
+           argc = __builtin_expect (argc, 100);
+           return argv[argc != 100][0];
+         }]])],
+       [gl_cv___builtin_expect=yes],
+       [AC_LINK_IFELSE(
+          [AC_LANG_SOURCE([[
+             #include <builtins.h>
+             int
+             main (int argc, char **argv)
+             {
+               argc = __builtin_expect (argc, 100);
+               return argv[argc != 100][0];
+             }]])],
+          [gl_cv___builtin_expect="in <builtins.h>"],
+          [gl_cv___builtin_expect=no])])])
+  if test "$gl_cv___builtin_expect" = yes; then
+    AC_DEFINE([HAVE___BUILTIN_EXPECT], [1])
+  elif test "$gl_cv___builtin_expect" = "in <builtins.h>"; then
+    AC_DEFINE([HAVE___BUILTIN_EXPECT], [2])
+  fi
+  AH_VERBATIM([HAVE___BUILTIN_EXPECT],
+    [/* Define to 1 if the compiler supports __builtin_expect,
+   and to 2 if <builtins.h> does.  */
+#undef HAVE___BUILTIN_EXPECT
+#ifndef HAVE___BUILTIN_EXPECT
+# define __builtin_expect(e, c) (e)
+#elif HAVE___BUILTIN_EXPECT == 2
+# include <builtins.h>
+#endif
+    ])
+])