pgsql: Allow UNIQUE indexes on partitioned tables

Allow UNIQUE indexes on partitioned tables

If we restrict unique constraints on partitioned tables so that they
must always include the partition key, then our standard approach to
unique indexes already works --- each unique key is forced to exist
within a single partition, so enforcing the unique restriction in each
index individually is enough to have it enforced globally.  Therefore we
can implement unique indexes on partitions by simply removing a few
restrictions (and adding others.)

Discussion: https://postgr.es/m/20171222212921.hi6hg6pem2w2t36z@alvherre.pgsql
Discussion: https://postgr.es/m/20171229230607.3iib6b62fn3uaf47@alvherre.pgsql
Reviewed-by: Simon Riggs, Jesper Pedersen, Peter Eisentraut, Jaime
        Casanova, Amit Langote

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/eb7ed3f3063401496e4aa4bd68fa33f0be31a72f

Modified Files
--------------
doc/src/sgml/ddl.sgml                         |   9 +-
doc/src/sgml/ref/alter_table.sgml             |  15 +-
doc/src/sgml/ref/create_index.sgml            |   5 +
doc/src/sgml/ref/create_table.sgml            |  18 +-
src/backend/bootstrap/bootparse.y             |   2 +
src/backend/catalog/index.c                   |  50 ++++-
src/backend/catalog/pg_constraint.c           |  76 +++++++
src/backend/catalog/toasting.c                |   4 +-
src/backend/commands/indexcmds.c              | 125 +++++++++--
src/backend/commands/tablecmds.c              |  71 ++++++-
src/backend/parser/analyze.c                  |   7 +
src/backend/parser/parse_utilcmd.c            |  31 +--
src/backend/tcop/utility.c                    |   1 +
src/bin/pg_dump/t/002_pg_dump.pl              |  65 ++++++
src/include/catalog/index.h                   |   5 +-
src/include/catalog/pg_constraint_fn.h        |   4 +-
src/include/commands/defrem.h                 |   1 +
src/include/parser/parse_utilcmd.h            |   3 +-
src/test/regress/expected/alter_table.out     |   8 -
src/test/regress/expected/create_index.out    |   6 +
src/test/regress/expected/create_table.out    |  12 --
src/test/regress/expected/indexing.out        | 294 +++++++++++++++++++++++++-
src/test/regress/expected/insert_conflict.out |   2 +-
src/test/regress/sql/alter_table.sql          |   2 -
src/test/regress/sql/create_index.sql         |   6 +
src/test/regress/sql/create_table.sql         |   8 -
src/test/regress/sql/indexing.sql             | 172 ++++++++++++++-
27 files changed, 907 insertions(+), 95 deletions(-)