Make "usage" messages more helpful.

In case of incorrect command invocations U-Boot used to print pretty
useless "usage" messages, for example:

	=> nand markbad
	Usage:
	nand - NAND sub-system

In the result, the user would have to run the "help" command to get
the (available) information about correct command usage. Change this,
so that this information gets always printed.

Note that this changes the user interface of all commands, but
hopefully to the better.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/common/command.c b/common/command.c
index c9a3f5b..16f3afe 100644
--- a/common/command.c
+++ b/common/command.c
@@ -286,21 +286,7 @@
 	 */
 	for (i = 1; i < argc; ++i) {
 		if ((cmdtp = find_cmd_tbl (argv[i], cmd_start, cmd_items )) != NULL) {
-#ifdef	CONFIG_SYS_LONGHELP
-			/* found - print (long) help info */
-			puts (cmdtp->name);
-			putc (' ');
-			if (cmdtp->help) {
-				puts (cmdtp->help);
-			} else {
-				puts ("- No help available.\n");
-				rcode = 1;
-			}
-			putc ('\n');
-#else	/* no long help available */
-			if (cmdtp->usage)
-				printf ("%s - %s\n", cmdtp->name, cmdtp->usage);
-#endif	/* CONFIG_SYS_LONGHELP */
+			rcode |= cmd_usage(cmdtp);
 		} else {
 			printf ("Unknown command '%s' - try 'help'"
 				" without arguments for list of all"
@@ -386,9 +372,22 @@
 	return find_cmd_tbl(cmd, &__u_boot_cmd_start, len);
 }
 
-void cmd_usage(cmd_tbl_t *cmdtp)
+int cmd_usage(cmd_tbl_t *cmdtp)
 {
-	printf("Usage:\n%s - %s\n\n", cmdtp->name, cmdtp->usage);
+	printf("%s - %s\n\n", cmdtp->name, cmdtp->usage);
+
+#ifdef	CONFIG_SYS_LONGHELP
+	printf("Usage:\n%s ", cmdtp->name);
+
+	if (!cmdtp->help) {
+		puts ("- No additional help available.\n");
+		return 1;
+	}
+
+	puts (cmdtp->help);
+	putc ('\n');
+#endif	/* CONFIG_SYS_LONGHELP */
+	return 0;
 }
 
 #ifdef CONFIG_AUTO_COMPLETE