link,ln: use gnulib's link module to work around Solaris 10 deficiency

Before this change, :>f; ln -T f no-such/ would succeed on Solaris 10.
After it, ln fails, as it should: ln: accessing `z/': Not a directory
The command, link f no-such/, had the same problem on that system.
* bootstrap.conf (gnulib_modules): Add "link".
* tests/ln/slash-decorated-nonexistent-dest: New test.
* tests/Makefile.am (TESTS): Add it.
* NEWS (Portability): Mention the improvement.

NEWS

@@ -45,6 +45,14 @@ GNU coreutils NEWS                                    -*- outline -*-
   (i.e., not inotify-based) implementation.
   [bug introduced in coreutils-7.5]
 
+** Portability
+
+  ln, link: link f z/ would mistakenly succeed on Solaris 10, given an
+  existing file, f, and nothing named "z".  ln -T f z/ has the same problem.
+  Each would mistakenly create "z" as a link to "f".  Now, even on such a
+  system, each command reports the error, e.g.,
+  link: cannot create link `z/' to `f': Not a directory
+
 ** New features
 
   cp --reflink accepts a new "auto" parameter which falls back to

bootstrap.conf

@@ -130,6 +130,7 @@ gnulib_modules="
   lchown
   lib-ignore
   linebuffer
+  link
   link-follow
   long-options
   lstat

tests/Makefile.am

@@ -345,6 +345,7 @@ TESTS =						\
   ln/hard-backup				\
   ln/misc					\
   ln/sf-1					\
+  ln/slash-decorated-nonexistent-dest		\
   ln/target-1					\
   ls/abmon-align				\
   ls/color-clear-to-eol				\

tests/ln/slash-decorated-nonexistent-dest

@@ -0,0 +1,34 @@
+#!/bin/sh
+# ensure that touch f; ln -T f no-such-file/ does not mistakenly succeed
+
+# Copyright (C) 2009 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/>.
+
+if test "$VERBOSE" = yes; then
+  set -x
+  ln --version
+fi
+
+. $srcdir/test-lib.sh
+
+touch f || framework_failure
+
+fail=0
+
+# Before coreutils-7.6, this would succeed on Solaris 10
+ln -T f no-such-file/ && fail=1
+test -e no-such-file && fail=1
+
+Exit $fail