Re: pg_resetwal tests, logging, and docs update

Hi,

> I noticed that pg_resetwal has poor test coverage. There are some TAP
> tests, but they all run with -n, so they don't actually test the full
> functionality. (There is a non-dry-run call of pg_resetwal in the
> recovery test suite, but that is incidental.)
>
> So I added a bunch of more tests to test all the different options and
> scenarios. That also led to adding more documentation about more
> details how some of the options behave, and some tweaks in the program
> output.
>
> It's attached as one big patch, but it could be split into smaller
> pieces, depending what gets agreement.

All in all the patch looks OK but I have a couple of nitpicks.

```
+ working on a data directory in an unclean shutdown state or with a corrupt
+ control file.
```

```
+ After running this command on a data directory with corrupted WAL or a
+ corrupt control file,
```

I'm not a native English speaker but shouldn't it be "corruptED control file"?

```
+ Force <command>pg_resetwal</command> to proceed even in situations where
+ it could be dangerous,
```

"where" is probably fine but wouldn't "WHEN it could be dangerous" be better?

```
+ // FIXME: why 2?
if (set_oldest_commit_ts_xid < 2 &&
```

Should we rewrite this to < FrozenTransactionId ?

```
+$mult = 32 * $blcksz * 4; # FIXME
```

Unless I'm missing something this $mult value is not used. Is it
really needed here?

--
Best regards,
Aleksander Alekseev