Work around a readdir bug in Darwin 7.9.0 (MacOS X 10.3.9) on HFS+

and NFS, whereby rm would not remove all files in a directory.
* src/remove.c (CONSECUTIVE_READDIR_UNLINK_THRESHOLD): Reduce to 10.
(NEED_REWIND): New macro, so that we incur the cost of the work-around
rewinddir only on afflicted systems.
* NEWS: Clarify and correct.
* tests/rm/readdir-bug: New file.  Test for the above fix.
* tests/rm/Makefile.am (TESTS): Add it.
Prompted by testing and analysis from Bruno Haible:
http://lists.gnu.org/archive/html/bug-coreutils/2006-09/msg00326.html

tests/rm/Makefile.am

@@ -21,6 +21,7 @@
 AUTOMAKE_OPTIONS = 1.1 gnits
 
 TESTS = \
+  readdir-bug \
   empty-inacc \
   dir-nonrecur \
   dot-rel \

tests/rm/readdir-bug

@@ -0,0 +1,60 @@
+#!/bin/sh
+# Exercise the Darwin/MacOS bug worked around on 2006-09-29,
+# whereby rm would fail to remove all entries in a directory.
+
+# Copyright (C) 2006 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 2 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, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+if test "$VERBOSE" = yes; then
+  set -x
+  rm --version
+fi
+
+pwd=`pwd`
+t0=`echo "$0"|sed 's,.*/,,'`.tmp; tmp=$t0/$$
+trap 'status=$?; cd $pwd; chmod -R u+rwx $t0; rm -rf $t0 && exit $status' 0
+trap '(exit $?); exit $?' 1 2 13 15
+
+framework_failure=0
+mkdir -p $tmp || framework_failure=1
+cd $tmp || framework_failure=1
+
+# Create a directory containing many files.
+# What counts is a combination of the number of files and
+# the lengths of their names.  For details, see
+# http://lists.gnu.org/archive/html/bug-coreutils/2006-09/msg00326.html
+mkdir b || framework_failure=1
+cd b || framework_failure=1
+for i in $(seq 1 250); do
+  touch $(printf %040d $i) || framework_failure=1
+done
+cd .. || framework_failure=1
+
+if test $framework_failure = 1; then
+  echo "$0: failure in testing framework" 1>&2
+  (exit 1); exit 1
+fi
+
+fail=0
+
+# On a buggy system, this would fail with the diagnostic,
+# "cannot remove directory `b': Directory not empty"
+rm -rf b  || fail=1
+
+test -d b && fail=1
+
+(exit $fail); exit $fail