pgsql: Allow ON CONFLICT .. DO NOTHING on a partitioned table.

Allow ON CONFLICT .. DO NOTHING on a partitioned table.

ON CONFLICT .. DO UPDATE still doesn't work, for lack of a way of
enforcing uniqueness across partitions, but we can still allow this
case.

Amit Langote, per discussion with Peter Geoghegan.  Additional
wordsmithing by me.

Discussion: http://postgr.es/m/CAA-aLv7Z4uygtq-Q5CvDi9Y=VZxUyEnuWjL=EwCfOof=L04hgg@mail.gmail.com

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/8355a011a0124bdf7ccbada206a967d427039553

Modified Files
--------------
doc/src/sgml/ddl.sgml                         |  8 ++++++--
src/backend/parser/analyze.c                  |  8 --------
src/test/regress/expected/insert_conflict.out | 10 ++++++++++
src/test/regress/sql/insert_conflict.sql      | 10 ++++++++++
4 files changed, 26 insertions(+), 10 deletions(-)