Implementation of tag command.

+/* GNU mailutils - a suite of utilities for electronic mail
+   Copyright (C) 1999, 2001 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, 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., 675 Mass Ave, Cambridge, MA 02139, USA.  */
+
+#include "mail.h"
+
+/* ta[g] [msglist] */
+/* unt[ag] [msglist] */
+
+static int
+tag_message (message_t mesg, msgset_t *msgset, int *action)
+{
+  attribute_t attr;
+
+  message_get_attribute (mesg, &attr);
+  if (*action)
+    attribute_set_userflag (attr, MAIL_ATTRIBUTE_TAGGED);
+  else
+    attribute_unset_userflag (attr, MAIL_ATTRIBUTE_TAGGED);
+  return 0;
+}
+
+int
+mail_tag (int argc, char **argv)
+{
+  msgset_t *msgset;
+  int action = argv[0][0] != 'u';
+  
+  if (msgset_parse (argc, argv, &msgset))
+    return 1;
+
+  util_msgset_iterate (msgset, tag_message, &action);
+
+  msgset_free (msgset);
+  return 0;
+}
+