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/putenv.m4

@@ -0,0 +1,56 @@
+# putenv.m4 serial 20
+dnl Copyright (C) 2002-2017 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 From Jim Meyering.
+dnl
+dnl Check whether putenv ("FOO") removes FOO from the environment.
+dnl The putenv in libc on at least SunOS 4.1.4 does *not* do that.
+
+AC_DEFUN([gl_FUNC_PUTENV],
+[
+  AC_REQUIRE([gl_STDLIB_H_DEFAULTS])
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+  AC_CACHE_CHECK([for putenv compatible with GNU and SVID],
+   [gl_cv_func_svid_putenv],
+   [AC_RUN_IFELSE([AC_LANG_PROGRAM([AC_INCLUDES_DEFAULT],[[
+    /* Put it in env.  */
+    if (putenv ("CONFTEST_putenv=val"))
+      return 1;
+
+    /* Try to remove it.  */
+    if (putenv ("CONFTEST_putenv"))
+      return 2;
+
+    /* Make sure it was deleted.  */
+    if (getenv ("CONFTEST_putenv") != 0)
+      return 3;
+
+    return 0;
+              ]])],
+             gl_cv_func_svid_putenv=yes,
+             gl_cv_func_svid_putenv=no,
+             dnl When crosscompiling, assume putenv is broken.
+             [case "$host_os" in
+                        # Guess yes on glibc systems.
+                *-gnu*) gl_cv_func_svid_putenv="guessing yes" ;;
+                        # If we don't know, assume the worst.
+                *)      gl_cv_func_svid_putenv="guessing no" ;;
+              esac
+             ])
+   ])
+  case "$gl_cv_func_svid_putenv" in
+    *yes) ;;
+    *)
+      REPLACE_PUTENV=1
+      ;;
+  esac
+])
+
+# Prerequisites of lib/putenv.c.
+AC_DEFUN([gl_PREREQ_PUTENV],
+[
+  AC_CHECK_DECLS([_putenv])
+])