use strbuf_addbuf() for appending a strbuf to another

Use strbuf_addbuf() where possible; it's shorter and more efficient.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

path.c

@@ -246,7 +246,7 @@ static void do_submodule_path(struct strbuf *buf, const char *path,
 		strbuf_addstr(buf, git_dir);
 	}
 	strbuf_addch(buf, '/');
-	strbuf_addstr(&git_submodule_dir, buf->buf);
+	strbuf_addbuf(&git_submodule_dir, buf);
 
 	strbuf_vaddf(buf, fmt, args);