RE: Force streaming every change in logical decoding

Dear Amit,

Thank you for updating the patch. I have also checked the patch
and basically it has worked well. Almost all things I found were modified
by v4.

One comment: while setting logical_decoding_mode to wrong value,
I got unfriendly ERROR message.

```
postgres=# SET logical_decoding_mode = 1;
ERROR:  invalid value for parameter "logical_decoding_mode": "1"
HINT:  Available values: , immediate
```

Here all acceptable enum should be output as HINT, but we could not see the empty string.
Should we modify config_enum_get_options() for treating empty string, maybe
like (empty)? Or we can ignore now.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED