Partitioning syntax

Here is a revised partitioning syntax patch. It implements only syntax and
on-disk structure mentioned below:
    Table Partitioning#Syntax
      http://wiki.postgresql.org/wiki/Table_partitioning#Syntax
    Table Partitioning#On-disk structure
      http://wiki.postgresql.org/wiki/Table_partitioning#On-disk_structure

What we can do with the patch is src/test/regress/sql/partition.sql.
Note that the patch does nothing about INSERTs; triggers are still needed.

The main syntax is CREATE TABLE () PARTITION BY {RANGE | LIST} (...).
The reason I use it rather than "PARTITIONED BY" is for compatibility
to other DBMSs; Oracle and MySQL.

Changes from the previous CommitFest are:
 - Additinal regression tests:
   1000 partitions, error cases and boolean partitions
 - Use pg_inherits_parent_index index if available.
 - Sort not only range partitions but also list partitions
   for stable display order.
 - Remove ALTER PARTITION and DROP PARTITION syntax because
   they are just synonyms of ALTER TABLE and DROP TABLE.

Regards,
---
Takahiro Itagaki
NTT Open Source Software Center