Make pg_checksums complain if compiled BLCKSZ and data folder's block size differ

Hi all,
(related folks in CC)

Sergei Kornilov has reported here an issue with pg_checksums:
https://www.postgresql.org/message-id/5217311552474471@myt2-66bcb87429e6.qloud-c.yandex.net

If the block size the tool is compiled with does not match the data
folder block size, then users would get incorrect checksums failures,
which is confusing.  As pg_checksum_block() uses directly the block
size, this cannot really be made dynamic yet, so we had better issue
an error on that.  Michael Banck has sent a patch for that:
https://www.postgresql.org/message-id/1552476561.4947.67.camel@credativ.de

The error message proposed is like that:
+   if (ControlFile->blcksz != BLCKSZ)
+   {
+       fprintf(stderr, _("%s: data directory block size %d is different to compiled-in block size %d.\n"),
+               progname, ControlFile->blcksz, BLCKSZ);
+       exit(1);
+   }
Still I think that we could do better.

Here is a proposal of message which looks more natural to me, and more
consistent with what xlog.c complains about:
database files are incompatible with pg_checksums.
The database cluster was initialized with BLCKSZ %d, but pg_checksums
was compiled with BLCKSZ %d.

Has somebody a better wording for that?  Attached is a proposal of
patch.
--
Michael