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/environ.m4

@@ -0,0 +1,47 @@
+# environ.m4 serial 6
+dnl Copyright (C) 2001-2004, 2006-2017 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.
+
+AC_DEFUN_ONCE([gl_ENVIRON],
+[
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  dnl Persuade glibc <unistd.h> to declare environ.
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
+  AC_CHECK_HEADERS_ONCE([unistd.h])
+  gt_CHECK_VAR_DECL(
+    [#if HAVE_UNISTD_H
+     #include <unistd.h>
+     #endif
+     /* mingw, BeOS, Haiku declare environ in <stdlib.h>, not in <unistd.h>.  */
+     #include <stdlib.h>
+    ],
+    [environ])
+  if test $gt_cv_var_environ_declaration != yes; then
+    HAVE_DECL_ENVIRON=0
+  fi
+])
+
+# Check if a variable is properly declared.
+# gt_CHECK_VAR_DECL(includes,variable)
+AC_DEFUN([gt_CHECK_VAR_DECL],
+[
+  define([gt_cv_var], [gt_cv_var_]$2[_declaration])
+  AC_MSG_CHECKING([if $2 is properly declared])
+  AC_CACHE_VAL([gt_cv_var], [
+    AC_COMPILE_IFELSE(
+      [AC_LANG_PROGRAM(
+         [[$1
+           extern struct { int foo; } $2;]],
+         [[$2.foo = 1;]])],
+      [gt_cv_var=no],
+      [gt_cv_var=yes])])
+  AC_MSG_RESULT([$gt_cv_var])
+  if test $gt_cv_var = yes; then
+    AC_DEFINE([HAVE_]m4_translit($2, [a-z], [A-Z])[_DECL], 1,
+              [Define if you have the declaration of $2.])
+  fi
+  undefine([gt_cv_var])
+])