remote-{ext,fd}: print usage message on invalid arguments

We just say "Expected two arguments" when we get a different
number of arguments, but we can be slightly friendlier.
People shouldn't generally be running remote helpers
themselves, but curious users might say "git remote-ext -h".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/remote-ext.c

@@ -3,6 +3,9 @@
 #include "run-command.h"
 #include "pkt-line.h"
 
+static const char usage_msg[] =
+	"git remote-ext <remote> <url>";
+
 /*
  * URL syntax:
  *	'command [arg1 [arg2 [...]]]'	Invoke command with given arguments.
@@ -193,7 +196,7 @@ static int command_loop(const char *child)
 int cmd_remote_ext(int argc, const char **argv, const char *prefix)
 {
 	if (argc != 3)
-		die("Expected two arguments");
+		usage(usage_msg);
 
 	return command_loop(argv[2]);
 }

builtin/remote-fd.c

@@ -1,6 +1,9 @@
 #include "builtin.h"
 #include "transport.h"
 
+static const char usage_msg[] =
+	"git remote-fd <remote> <url>";
+
 /*
  * URL syntax:
  *	'fd::<inoutfd>[/<anything>]'		Read/write socket pair
@@ -57,7 +60,7 @@ int cmd_remote_fd(int argc, const char **argv, const char *prefix)
 	char *end;
 
 	if (argc != 3)
-		die("Expected two arguments");
+		usage(usage_msg);
 
 	input_fd = (int)strtoul(argv[2], &end, 10);