Bigger patch for (partial) tinylogin integration

- Made a new dir loginutils
- Moved all applets from pwd_grp to loginutils
- Added new applets su.c login.c to loginutils
- Made a new dir libpwdgrp
- Moved everything from pwd_grp/libpwd_grp there
- Added shadow.c to libpwdgrp
- Removed dir pwd_grp
- Added usage strings for login and su to usage.h
- Changed main Makefile to reflect the dir rearrangements
[Parts of this patch may overlap with my other two patches]

libpwdgrp/getgrnam.c

@@ -0,0 +1,50 @@
+/*
+ * getgrnam.c - This file is part of the libc-8086/grp package for ELKS,
+ * Copyright (C) 1995, 1996 Nat Friedman <ndf@linux.mit.edu>.
+ * 
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Library General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2 of the License, or (at your option) any later version.
+ *
+ *  This library 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
+ *  Library General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Library General Public
+ *  License along with this library; if not, write to the Free
+ *  Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ */
+
+#include "busybox.h"
+
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include "grp.h"
+
+struct group *getgrnam(const char *name)
+{
+	int grp_fd;
+	struct group *group;
+
+	if (name == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	if ((grp_fd = open("/etc/group", O_RDONLY)) < 0)
+		return NULL;
+
+	while ((group = __getgrent(grp_fd)) != NULL)
+		if (!strcmp(group->gr_name, name)) {
+			close(grp_fd);
+			return group;
+		}
+
+	close(grp_fd);
+	return NULL;
+}