Audit logname(1)

1) Add usage().
2) Idiomatic argv0-setter. We don't use arg.h, as we do not process
   flags or arguments.
3) Remove program-name from eprintf-call. This is done in the eprintf-
   function itself when the DEBUG-define is set.
   We'll activate it by default later.
4) Add empty line before return.

README

@@ -41,7 +41,7 @@ The following tools are implemented ('*' == finished, '#' == UTF-8 support,
 =*| link            yes                          none
 =*| ln              yes                          none
 =*| logger          yes                          none
-=*  logname         yes                          none
+=*| logname         yes                          none
 =   ls              no                           (-C), -S, -f, -m, -s, -x
 =*| md5sum          non-posix                    none
 =*| mkdir           yes                          none

logname.c

@@ -4,17 +4,26 @@
 
 #include "util.h"
 
+static void
+usage(void)
+{
+	eprintf("usage: %s\n", argv0);
+}
+
 int
 main(int argc, char *argv[])
 {
 	char *login;
 
-	argv0 = argv[0];
-	if (argc != 1)
-		eprintf("usage: %s\n", argv0);
+	argv0 = argv[0], argc--, argv++;
+
+	if (argc)
+		usage();
+
 	if ((login = getlogin()))
 		puts(login);
 	else
-		eprintf("%s: no login name\n", argv0);
+		eprintf("no login name\n");
+
 	return 0;
 }