git-daemon: set REMOTE_ADDR to client address

This allows hooks like pre-receive to look at the client's IP
address.

Of course the IP address can't be used to get strong security;
git-daemon isn't the right thing to use if you need that. However,
basic IP address checking can be good enough in some situations.

REMOTE_ADDR is the same environment variable used to communicate the
client's address to CGI scripts.

Signed-off-by: Joey Hess <joey@kitenet.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

daemon.c

@@ -537,6 +537,10 @@ static int execute(struct sockaddr *addr)
 #endif
 		}
 		loginfo("Connection from %s:%d", addrbuf, port);
+		setenv("REMOTE_ADDR", addrbuf, 1);
+	}
+	else {
+		unsetenv("REMOTE_ADDR");
 	}
 
 	alarm(init_timeout ? init_timeout : timeout);