t5534: split stdout and stderr redirection

On atomic pushing failure with GnuPG, we expect a very specific output in stdout due to `--porcelain` switch. On such failure, we also write down some helpful hint into stderr in order to help user understand what happens and how to continue from those failures. On a lot of system, those hint (in stderr) will be flushed first, then those messages in stdout will be flushed. In such systems, the current test code is fine as is. However, we don't have such guarantee, (at least) there're some real systems that writes those stream interleaved. On such systems, we may see the stderr stream written in the middle of stdout stream. Let's split those stream redirection. By splitting those stream, the output stream will contain exactly what we want to compare, thus, saving us a "sed" invocation. While we're at it, change the `test_i18ncmp` to `test_cmp` because we will never translate those messages (because of `--porcelain`). Signed-off-by: Đoàn Trần Công Danh <congdanhqx@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>