Fix --test-label' and --label -r' behavior.

* doc/tar.texi (Including a Label in the Archive): Revise
the section.
* NEWS: Update

* src/buffer.c (open_archive): Check volume label on
ACCESS_UPDATE as well.
* src/list.c (test_archive_label): Rewrite to match the
documentation.
* src/names.c (regex_usage_warning): Return int.
(names_notfound): Rewrite the conditional.
(label_notfound): New function.

* tests/label03.at: New testcase.
* tests/label04.at: New testcase.
* tests/label05.at: New testcase.
* tests/Makefile.am: Add new testcases.
* tests/testsuite.at: Likewise.

tests/label05.at

@@ -0,0 +1,50 @@
+# 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, see <http://www.gnu.org/licenses/>.
+
+# Description: See label04.  This testcase uses an unlabeled archive
+# volume.
+
+AT_SETUP([label with non-create option])
+AT_KEYWORDS([label label05])
+
+AT_TAR_CHECK([
+exec <&-
+genfile --file file
+decho "# Create volume"
+tar -c -f archive file
+decho "# Update: wrong label"
+tar -rf archive --label='My volume' file; echo $?
+decho "# Update: right label"
+tar -rf archive file
+],
+[0],
+[# Create volume
+# Update: wrong label
+2
+# Update: right label
+],
+[# Create volume
+# Update: wrong label
+tar: Archive not labeled to match `My volume'
+tar: Error is not recoverable: exiting now
+# Update: right label
+],[],[],[gnu,oldgnu,posix])
+
+AT_CLEANUP
+
+