tar: handle files that occur multiple times but have link count 1

This patch was inspired by the following patch that addressed a
similar problem in GNU coreutils du:
http://git.savannah.gnu.org/gitweb/?p=coreutils.git;h=efe53cc72b599979ea292754ecfe8abf7c839d22
* src/common.h (name_count): New decl.
* src/create.c (trivial_link_count): New static var.
(create_archive): Initialize it.
(dump_hard_link, file_count_links): Use it, so that files with
link count 1 are handled correctly when they are found multiple times.
* src/names.c (allocated_entries): Renamed from allocated_names,
since the identifier's name was misleading.  All uses changed.
(entries): Renamed from names.  All uses changed.
(scanned): Renamed from name_index.  All uses changed.
(name_count): New var.
(name_add_name): Increment it.
* tests/link04.at: New file.
* tests/testsuite.at: Add it.
* tests/Makefile.am (TESTSUITE_AT): Likewise.

tests/Makefile.am

@@ -97,6 +97,7 @@ TESTSUITE_AT = \
  link01.at\
  link02.at\
  link03.at\
+ link04.at\
  listed01.at\
  listed02.at\
  listed03.at\

tests/link04.at

@@ -0,0 +1,58 @@
+# Process this file with autom4te to create testsuite. -*- Autotest -*-
+
+# Test suite for GNU tar.
+# Copyright (C) 2010 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, 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.
+
+# written by Paul Eggert
+
+AT_SETUP([link count is 1 but multiple occurrences])
+AT_KEYWORDS([hardlinks link04])
+
+AT_TAR_CHECK([
+mkdir dir
+echo TEST > dir/file
+ln -s file dir/symlink || AT_SKIP_TEST
+
+tar cf archive dir dir
+tar tvf archive | sed '
+  s,.*[[0-9]] dir/,dir/,
+' | sort
+
+echo ==
+
+tar chf archive dir
+tar tvf archive | sed '
+  s,.*[[0-9]] dir/,dir/,
+  s,file,FOO,g
+  s,symlink,FOO,g
+' | sort
+],
+[0],
+[dir/
+dir/
+dir/file
+dir/file link to dir/file
+dir/symlink -> file
+dir/symlink link to dir/symlink
+==
+dir/
+dir/FOO
+dir/FOO link to dir/FOO
+])
+
+AT_CLEANUP

tests/testsuite.at

@@ -184,6 +184,7 @@ m4_include([ignfail.at])
 m4_include([link01.at])
 m4_include([link02.at])
 m4_include([link03.at])
+m4_include([link04.at])
 
 m4_include([longv7.at])
 m4_include([long01.at])