pgsql: Exclude backup_manifest file that existed in database, from BASE

Exclude backup_manifest file that existed in database, from BASE_BACKUP.

If there is already a backup_manifest file in the database cluster,
it belongs to the past backup that was used to start this server.
It is not correct for the backup being taken now. So this commit
changes pg_basebackup so that it always skips such backup_manifest
file. The backup_manifest file for the current backup will be injected
separately if users want it.

Author: Fujii Masao
Reviewed-by: Robert Haas
Discussion: https://postgr.es/m/78f76a3d-1a28-a97d-0394-5c96985dd1c0@oss.nttdata.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1ec50a81ec0acd452c7520de19e607a6de8fba5e

Modified Files
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src/backend/replication/basebackup.c | 8 ++++++++
src/bin/pg_rewind/filemap.c          | 8 ++++++++
2 files changed, 16 insertions(+)