pgsql: pg_checksums: Use new routine to retrieve data of PG_VERSION

pg_checksums: Use new routine to retrieve data of PG_VERSION

Previously, attempting to use pg_checksums on a cluster with a control
file whose version does not match with what thetool is able to support
would lead to the following error:
pg_checksums: error: pg_control CRC value is incorrect

This is confusing, because it would look like the control file is
corrupted. However, the contents of the control file are correct,
pg_checksums not being able to understand how the past control file is
shaped.

This commit adds a check based on PG_VERSION, using the facility added
by cd0be131ba6f, using the same error message as some of the other
frontend tools. A note is added in the documentation about the major
version requirement.

Author: Michael Banck <mbanck(at)gmx(dot)net>
Discussion: https://postgr.es/m/68f1ff21.170a0220.2c9b5f.4df5@mx.google.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/a7c30422004ae757909ed831fd8eea453022f969

Modified Files
--------------
doc/src/sgml/ref/pg_checksums.sgml | 4 ++++
src/bin/pg_checksums/pg_checksums.c | 17 +++++++++++++++++
2 files changed, 21 insertions(+)