Bug #480 - @ Symbol in context not returning

- Fixed bug #480, which didn't properly support @ characters in tags.
  The problem was that the ctype.h ispunct() function considers @,
  # and $ to be punctuation, which I don't.  An override now allows
  these characters in tags, and specificallt '+@context' style tags.
- Added unit tests.

src/tests/bug.480.t

@@ -0,0 +1,75 @@
+#! /usr/bin/perl
+################################################################################
+## taskwarrior - a command line task list manager.
+##
+## Copyright 2006 - 2010, Paul Beckingham.
+## All rights reserved.
+##
+## 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
+##
+################################################################################
+
+use strict;
+use warnings;
+use Test::More tests => 13;
+
+# Create the rc file.
+if (open my $fh, '>', 'bug.rc')
+{
+  print $fh "data.location=.\n";
+
+  close $fh;
+  ok (-r 'bug.rc', 'Created bug.rc');
+}
+
+# Bug #480 - putting a '@' character in tags breaks filters.
+qx{../task rc:bug.rc add one +ordinary};
+qx{../task rc:bug.rc add two +\@strange};
+
+my $output = qx{../task rc:bug.rc long +ordinary};
+like ($output,   qr/one/, '+ordinary explicitly included');
+unlike ($output, qr/two/, '@strange implicitly excluded');
+
+$output = qx{../task rc:bug.rc long -ordinary};
+unlike ($output, qr/one/, '-ordinary explicitly excluded');
+like ($output,   qr/two/, '@strange implicitly included');
+
+$output = qx{../task rc:bug.rc long +\@strange};
+unlike ($output, qr/one/, '-ordinary implicitly excluded');
+like ($output,   qr/two/, '@strange explicitly included');
+
+$output = qx{../task rc:bug.rc long -\@strange};
+like ($output,   qr/one/, '+ordinary implicitly included');
+unlike ($output, qr/two/, '@strange explicitly excluded');
+
+# Cleanup.
+unlink 'pending.data';
+ok (!-r 'pending.data', 'Removed pending.data');
+
+unlink 'completed.data';
+ok (!-r 'completed.data', 'Removed completed.data');
+
+unlink 'undo.data';
+ok (!-r 'undo.data', 'Removed undo.data');
+
+unlink 'bug.rc';
+ok (!-r 'bug.rc', 'Removed bug.rc');
+
+exit 0;