RE: [Proposal] Adding Log File Capability to pg_createsubscriber

Hi,

While checking again, I found an issue in the new logging function - same va_list
is used twice, but it was the undefined behavior. va_copy() is used to fix the issue.

Also, below points were found and fixed in 0003. Thanks Peter Smith to work on.

```
+ printf(_(" -l, --logdir=LOGDIR location for the new log directory\n"));
```

But there is a possibility that existing directory is specified, right?

```
+my $logdir = PostgreSQL::Test::Utils::tempdir + "/logdir";
```

Isn't it enough to just use tempdir here? At least, I think using "+" is not
appropriate, "." is used to connect strings.

```
+ if (opt->log_dir != NULL)
+ appendPQExpBuffer(pg_ctl_cmd, " -l %s/%s/%s.log", opt->log_dir, log_timestamp, SERVER_LOG_FILE_NAME);
```

I do not have 100% confident, but do we have to quote the logfile here?

Best regards,
Hayato Kuroda
FUJITSU LIMITED