pgsql: In pg_upgrade, set synchronous_commit=off for the new cluster, t

In pg_upgrade, set synchronous_commit=off for the new cluster, to
improve performance when restoring the schema from the old cluster.

Backpatch to 9.2.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/ed5699dd1b883e193930448b7ad532e233de0bd7

Modified Files
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contrib/pg_upgrade/server.c | 11 ++++++++---
1 files changed, 8 insertions(+), 3 deletions(-)