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/readlink.m4

@@ -0,0 +1,71 @@
+# readlink.m4 serial 12
+dnl Copyright (C) 2003, 2007, 2009-2017 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([gl_FUNC_READLINK],
+[
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+  AC_CHECK_FUNCS_ONCE([readlink])
+  if test $ac_cv_func_readlink = no; then
+    HAVE_READLINK=0
+  else
+    AC_CACHE_CHECK([whether readlink signature is correct],
+      [gl_cv_decl_readlink_works],
+      [AC_COMPILE_IFELSE(
+         [AC_LANG_PROGRAM(
+           [[#include <unistd.h>
+      /* Cause compilation failure if original declaration has wrong type.  */
+      ssize_t readlink (const char *, char *, size_t);]])],
+         [gl_cv_decl_readlink_works=yes], [gl_cv_decl_readlink_works=no])])
+    dnl Solaris 9 ignores trailing slash.
+    dnl FreeBSD 7.2 dereferences only one level of links with trailing slash.
+    AC_CACHE_CHECK([whether readlink handles trailing slash correctly],
+      [gl_cv_func_readlink_works],
+      [# We have readlink, so assume ln -s works.
+       ln -s conftest.no-such conftest.link
+       ln -s conftest.link conftest.lnk2
+       AC_RUN_IFELSE(
+         [AC_LANG_PROGRAM(
+           [[#include <unistd.h>
+]], [[char buf[20];
+      return readlink ("conftest.lnk2/", buf, sizeof buf) != -1;]])],
+         [gl_cv_func_readlink_works=yes], [gl_cv_func_readlink_works=no],
+         [case "$host_os" in
+                    # Guess yes on glibc systems.
+            *-gnu*) gl_cv_func_readlink_works="guessing yes" ;;
+                    # If we don't know, assume the worst.
+            *)      gl_cv_func_readlink_works="guessing no" ;;
+          esac
+         ])
+      rm -f conftest.link conftest.lnk2])
+    case "$gl_cv_func_readlink_works" in
+      *yes)
+        if test "$gl_cv_decl_readlink_works" != yes; then
+          REPLACE_READLINK=1
+        fi
+        ;;
+      *)
+        AC_DEFINE([READLINK_TRAILING_SLASH_BUG], [1], [Define to 1 if readlink
+          fails to recognize a trailing slash.])
+        REPLACE_READLINK=1
+        ;;
+    esac
+  fi
+])
+
+# Like gl_FUNC_READLINK, except prepare for separate compilation
+# (no REPLACE_READLINK, no AC_LIBOBJ).
+AC_DEFUN([gl_FUNC_READLINK_SEPARATE],
+[
+  AC_CHECK_FUNCS_ONCE([readlink])
+  gl_PREREQ_READLINK
+])
+
+# Prerequisites of lib/readlink.c.
+AC_DEFUN([gl_PREREQ_READLINK],
+[
+  :
+])