pgsql: Add option to modify sync commit per subscription

Add option to modify sync commit per subscription

This also changes default behaviour of subscription workers to
synchronous_commit = off.

Author: Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com>

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/887227a1cc861d87ca0f175cf8bd1447554090eb

Modified Files
--------------
doc/src/sgml/catalogs.sgml | 10 ++++++
doc/src/sgml/ref/alter_subscription.sgml | 2 ++
doc/src/sgml/ref/create_subscription.sgml | 31 +++++++++++++++++
src/backend/catalog/pg_subscription.c | 8 +++++
src/backend/commands/subscriptioncmds.c | 54 +++++++++++++++++++++++++-----
src/backend/replication/logical/launcher.c | 6 +---
src/backend/replication/logical/worker.c | 8 +++++
src/bin/pg_dump/pg_dump.c | 11 +++++-
src/bin/pg_dump/pg_dump.h | 1 +
src/bin/psql/describe.c | 5 ++-
src/include/catalog/pg_subscription.h | 8 +++--
src/test/regress/expected/subscription.out | 30 ++++++++++-------
src/test/regress/sql/subscription.sql | 4 ++-
13 files changed, 145 insertions(+), 33 deletions(-)