Tweak logic for when to display:
Tweak logic for when to display:

  "Waiting for %d transactions to finish. First PID: %s"

message. Display it on every loop through the SQL_XID_ALIVE check
(i.e. every second), instead of only when the number of transactions
we're waiting on changes -- previously, it was too easy for that
important message to get lost in other messages.

And don't display the message at all when running under pg_regress,
i.e. as part of `make installcheck`. We had been getting occasional
errors from pg_regress when autovacuum was running and that message
got logged.

bwtakacy/pg_repack,mr-mustash/pg_repack,reorg/pg_repack,reorg/pg_repack