[PATCH] Log PostgreSQL version number on startup

Hi,

it has bugged me for a long time that there's no clear "PostgreSQL is
starting" message in the server log file. I'd like to change that for
two reasons:

* when reading a long log file, it's not entirely clear where a new
  server startup begins.

  It was worse in the past (first message was "database system was
  shut down at..." which rather looks like a shutdown message to
  newbie users), now it's "listening on IPv6..." but that message
  might possibly become DEBUG1, or listen_addresses might become
  changeable at run-time

* while upgrading servers, it's useful to know which server version
  was actually started if there are several startup attempts

The change would be to log "Starting PG_VERSION_STR" as early as
possible.

A startup looks like this:

2018-11-21 15:19:47.259 CET [24453] LOG:  listening on IPv6 address "::1", port 5431
2018-11-21 15:19:47.259 CET [24453] LOG:  listening on IPv4 address "127.0.0.1", port 5431
2018-11-21 15:19:47.315 CET [24453] LOG:  listening on Unix socket "/tmp/.s.PGSQL.5431"
2018-11-21 15:19:47.394 CET [24453] LOG:  starting PostgreSQL 12devel on x86_64-pc-linux-gnu, compiled by gcc (Debian
8.2.0-9)8.2.0, 64-bit
 
2018-11-21 15:19:47.426 CET [24454] LOG:  database system was shut down at 2018-11-21 15:15:35 CET
2018-11-21 15:19:47.460 CET [24453] LOG:  database system is ready to accept connections

(I'd rather put the start message before the listening messages, but I
think the startup message should be logged via logging_collector, and
listening is logged before the log file is opened.)

Christoph
-- 
Senior Berater, Tel.: +49 2166 9901 187
credativ GmbH, HRB Mönchengladbach 12080, USt-ID-Nummer: DE204566209
Trompeterallee 108, 41189 Mönchengladbach
Geschäftsführung: Dr. Michael Meskes, Jörg Folz, Sascha Heuer
Unser Umgang mit personenbezogenen Daten unterliegt
folgenden Bestimmungen: https://www.credativ.de/datenschutz