pgsql: pg_resetxlog: add option to set oldest xid & use by pg_upgrade

pg_resetxlog:  add option to set oldest xid & use by pg_upgrade

Add pg_resetxlog -u option to set the oldest xid in pg_control.
Previously -x set this value be -2 billion less than the -x value.
However, this causes the server to immediately scan all relation's
relfrozenxid so it can advance pg_control's oldest xid to be inside the
autovacuum_freeze_max_age range, which is inefficient and might disrupt
diagnostic recovery.  pg_upgrade will use this option to better create
the new cluster to match the old cluster.

Reported-by: Jason Harvey, Floris Van Nee

Discussion: https://postgr.es/m/20190615183759.GB239428@rfd.leadboat.com,
87da83168c644fd9aae38f546cc70295@opammb0562.comp.optiver.com

Author: Bertrand Drouvot

Backpatch-through: 9.6

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/71121450e8f42b21665ee9c8f70b701f7a16c801

Modified Files
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doc/src/sgml/ref/pg_resetwal.sgml | 19 +++++++++++++++++++
src/bin/pg_resetwal/pg_resetwal.c | 37 +++++++++++++++++++++++--------------
src/bin/pg_upgrade/controldata.c  | 17 ++++++++++++++++-
src/bin/pg_upgrade/pg_upgrade.c   |  7 +++++++
src/bin/pg_upgrade/pg_upgrade.h   |  1 +
5 files changed, 66 insertions(+), 15 deletions(-)