Re: HOT chain validation in verify_heapam()

Hi,

> Note that I have not tried any of this yet.

I did, both with Meson and Autotools. All in all the patch looks very
good, but I have a few little nitpicks.

```
+ /* HOT chains should not intersect. */
+ if (predecessor[nextoffnum] != InvalidOffsetNumber)
+ {
+ report_corruption(&ctx,
+ psprintf("redirect line pointer
points to offset %u, but offset %u also points there",
+ (unsigned) nextoffnum,
(unsigned) predecessor[nextoffnum]));
+ continue;
+ }
```

This type of corruption doesn't seem to be test-covered.

```
+ /*
+ * If the next line pointer is a redirect, or if it's a tuple
+ * but the XMAX of this tuple doesn't match the XMIN of the next
+ * tuple, then the two aren't part of the same update chain and
+ * there is nothing more to do.
+ */
+ if (ItemIdIsRedirected(next_lp))
+ continue;
```

lcov shows that the `continue` path is never executed. This is
probably not a big deal however.

```
+$node->append_conf('postgresql.conf','max_prepared_transactions=100');
```

From what I can tell this line is not needed.

--
Best regards,
Aleksander Alekseev