pgsql: Add pg_dump --snapshot option

Add pg_dump --snapshot option

Allows pg_dump to use a snapshot previously defined by a concurrent
session that has either used pg_export_snapshot() or obtained a
snapshot when creating a logical slot. When this option is used with
parallel pg_dump, the snapshot defined by this option is used and no
new snapshot is taken.

Simon Riggs and Michael Paquier

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/be1cc8f46f57a04e69d9e4dd268d34da885fe6eb

Modified Files
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doc/src/sgml/ref/pg_dump.sgml | 21 +++++++++++++++++
src/bin/pg_dump/pg_dump.c | 51 +++++++++++++++++++++++++++--------------
2 files changed, 55 insertions(+), 17 deletions(-)