[HACKERS] Adding support for Default partition in partitioning

partitioned table as follows.

postgres=# CREATE TABLE list_partitioned (              
    a int
) PARTITION BY LIST (a);
CREATE TABLE

postgres=# CREATE TABLE part_default PARTITION OF list_partitioned FOR VALUES IN (DEFAULT);
CREATE TABLE

postgres=# CREATE TABLE part_1 PARTITION OF list_partitioned FOR VALUES IN (4,5);
CREATE TABLE

postgres=# insert into list_partitioned values (9);
INSERT 0 1

postgres=# select * from part_default;
 a
---
 9
(1 row)

The attached patch is in a  preliminary stage and has following ToDos:

1. Adding pg_dump support.

2. Documentation

3. Handling adding a new partition to a partitioned table

Thank you,

Rahila Syed