pgsql: postgres_fdw: When sending ORDER BY, always include NULLS FIRST/

postgres_fdw: When sending ORDER BY, always include NULLS FIRST/LAST.

Previously, we included NULLS FIRST when appropriate but relied on the
default behavior to be NULLS LAST.  This is, however, not true for a
sort in descending order and seems like a fragile assumption anyway.

Report by Rajkumar Raghuwanshi.  Patch by Ashutosh Bapat.  Review
comments from Michael Paquier and Tom Lane.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/3bea3f88d5fc3517042ba83d2906979256da2442

Modified Files
--------------
contrib/postgres_fdw/deparse.c                 |   2 +
contrib/postgres_fdw/expected/postgres_fdw.out | 142 +++++++++++++++++++------
contrib/postgres_fdw/sql/postgres_fdw.sql      |  12 +++
3 files changed, 125 insertions(+), 31 deletions(-)