RE: Slot's restart_lsn may point to removed WAL segment after hard restart unexpectedly

Dear Alexander,

Thanks for pushing the fix patch! BTW, I have few comments for your commits.
Can you check and include them if needed?

01.
```
$node->append_conf('postgresql.conf',
    "shared_preload_libraries = 'injection_points'");
```

No need to set shared_preload_libraries in 046/047. ISTM it must be set when we
enable the statistics.

02.
We should also check whether the injection_points can be installed or not.
You can check check_extension() and callers.

Best regards,
Hayato Kuroda
FUJITSU LIMITED