pgsql: Check that the pg_upgrade user specified is a super-user.

Check that the pg_upgrade user specified is a super-user.

Also report the error message when the post-pg_ctl connection fails.

Per private bug report from EnterpriseDB.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/81301b85781245676f874ae3908015f05d3aaaa2

Modified Files
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contrib/pg_upgrade/check.c | 29 ++++++++++++++++++++++++++++-
contrib/pg_upgrade/server.c | 6 ++++--
2 files changed, 32 insertions(+), 3 deletions(-)