pgsql: Allow CHECK constraints to be placed on foreign tables.

Allow CHECK constraints to be placed on foreign tables.

As with NOT NULL constraints, we consider that such constraints are merely
reports of constraints that are being enforced by the remote server (or
other underlying storage mechanism). Their only real use is to allow
planner optimizations, for example in constraint-exclusion checks. Thus,
the code changes here amount to little more than removal of the error that
was formerly thrown for applying CHECK to a foreign table.

(In passing, do a bit of cleanup of the ALTER FOREIGN TABLE reference page,
which had accumulated some weird decisions about ordering etc.)

Shigeru Hanada and Etsuro Fujita, reviewed by Kyotaro Horiguchi and
Ashutosh Bapat.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/fc2ac1fb41c2defb8caf825781af75db158fb7a9

Modified Files
--------------
contrib/file_fdw/input/file_fdw.source | 16 +++-
contrib/file_fdw/output/file_fdw.source | 32 ++++++-
contrib/postgres_fdw/expected/postgres_fdw.out | 85 ++++++++++++++++++
contrib/postgres_fdw/sql/postgres_fdw.sql | 30 +++++++
doc/src/sgml/ref/alter_foreign_table.sgml | 113 ++++++++++++++++++------
doc/src/sgml/ref/create_foreign_table.sgml | 65 +++++++++++++-
src/backend/catalog/heap.c | 9 +-
src/backend/commands/tablecmds.c | 8 +-
src/backend/parser/parse_utilcmd.c | 51 ++++++++---
src/test/regress/expected/foreign_data.out | 57 ++++++++++--
src/test/regress/sql/foreign_data.sql | 28 +++++-
11 files changed, 432 insertions(+), 62 deletions(-)