Implement table partitioning.

Table partitioning is like table inheritance and reuses much of the
existing infrastructure, but there are some important differences.
The parent is called a partitioned table and is always empty; it may
not have indexes or non-inherited constraints, since those make no
sense for a relation with no data of its own.  The children are called
partitions and contain all of the actual data.  Each partition has an
implicit partitioning constraint.  Multiple inheritance is not
allowed, and partitioning and inheritance can't be mixed.  Partitions
can't have extra columns and may not allow nulls unless the parent
does.  Tuples inserted into the parent are automatically routed to the
correct partition, so tuple-routing ON INSERT triggers are not needed.
Tuple routing isn't yet supported for partitions which are foreign
tables, and it doesn't handle updates that cross partition boundaries.

Currently, tables can be range-partitioned or list-partitioned.  List
partitioning is limited to a single column, but range partitioning can
involve multiple columns.  A partitioning "column" can be an
expression.

Because table partitioning is less general than table inheritance, it
is hoped that it will be easier to reason about properties of
partitions, and therefore that this will serve as a better foundation
for a variety of possible optimizations, including query planner
optimizations.  The tuple routing based which this patch does based on
the implicit partitioning constraints is an example of this, but it
seems likely that many other useful optimizations are also possible.

Amit Langote, reviewed and tested by Robert Haas, Ashutosh Bapat,
Amit Kapila, Rajkumar Raghuwanshi, Corey Huinker, Jaime Casanova,
Rushabh Lathia, Erik Rijkers, among others.  Minor revisions by me.

src/test/regress/sql/insert.sql

@@ -84,3 +84,89 @@ create rule irule3 as on insert to inserttest2 do also
 drop table inserttest2;
 drop table inserttest;
 drop type insert_test_type;
+
+-- direct partition inserts should check partition bound constraint
+create table range_parted (
+	a text,
+	b int
+) partition by range (a, (b+0));
+create table part1 partition of range_parted for values from ('a', 1) to ('a', 10);
+create table part2 partition of range_parted for values from ('a', 10) to ('a', 20);
+create table part3 partition of range_parted for values from ('b', 1) to ('b', 10);
+create table part4 partition of range_parted for values from ('b', 10) to ('b', 20);
+
+-- fail
+insert into part1 values ('a', 11);
+insert into part1 values ('b', 1);
+-- ok
+insert into part1 values ('a', 1);
+-- fail
+insert into part4 values ('b', 21);
+insert into part4 values ('a', 10);
+-- ok
+insert into part4 values ('b', 10);
+
+-- fail (partition key a has a NOT NULL constraint)
+insert into part1 values (null);
+-- fail (expression key (b+0) cannot be null either)
+insert into part1 values (1);
+
+create table list_parted (
+	a text,
+	b int
+) partition by list (lower(a));
+create table part_aa_bb partition of list_parted FOR VALUES IN ('aa', 'bb');
+create table part_cc_dd partition of list_parted FOR VALUES IN ('cc', 'dd');
+create table part_null partition of list_parted FOR VALUES IN (null);
+
+-- fail
+insert into part_aa_bb values ('cc', 1);
+insert into part_aa_bb values ('AAa', 1);
+insert into part_aa_bb values (null);
+-- ok
+insert into part_cc_dd values ('cC', 1);
+insert into part_null values (null, 0);
+
+-- check in case of multi-level partitioned table
+create table part_ee_ff partition of list_parted for values in ('ee', 'ff') partition by range (b);
+create table part_ee_ff1 partition of part_ee_ff for values from (1) to (10);
+create table part_ee_ff2 partition of part_ee_ff for values from (10) to (20);
+
+-- fail
+insert into part_ee_ff1 values ('EE', 11);
+-- fail (even the parent's, ie, part_ee_ff's partition constraint applies)
+insert into part_ee_ff1 values ('cc', 1);
+-- ok
+insert into part_ee_ff1 values ('ff', 1);
+insert into part_ee_ff2 values ('ff', 11);
+
+-- Check tuple routing for partitioned tables
+
+-- fail
+insert into range_parted values ('a', 0);
+-- ok
+insert into range_parted values ('a', 1);
+insert into range_parted values ('a', 10);
+-- fail
+insert into range_parted values ('a', 20);
+-- ok
+insert into range_parted values ('b', 1);
+insert into range_parted values ('b', 10);
+-- fail (partition key (b+0) is null)
+insert into range_parted values ('a');
+select tableoid::regclass, * from range_parted;
+
+-- ok
+insert into list_parted values (null, 1);
+insert into list_parted (a) values ('aA');
+-- fail (partition of part_ee_ff not found in both cases)
+insert into list_parted values ('EE', 0);
+insert into part_ee_ff values ('EE', 0);
+-- ok
+insert into list_parted values ('EE', 1);
+insert into part_ee_ff values ('EE', 10);
+select tableoid::regclass, * from list_parted;
+
+-- cleanup
+drop table range_parted cascade;
+drop table list_parted cascade;