Re: Support logical replication of DDLs

I applied patch 0005.

I think this modification is a bit overdone.
This design skips all subcommands, which results in many ddl
replication failures.
For example:
```
CREATE TABLE datatype_table (id SERIAL);
```
deparsed ddl is:
CREATE TABLE public.datatype_table (id pg_catalog.int4 STORAGE plain
NOT NULL DEFAULT
pg_catalog.nextval('public.datatype_table_id_seq'::pg_catalog.regclass))
CREATE SEQUENCE subcommand will be skipped.

OR:
```
CREATE SCHEMA element_test
CREATE TABLE foo (id int)
CREATE VIEW bar AS SELECT * FROM foo;
```
deparsed ddl is:
CREATE SCHEMA element_test.

Its subcommands will be skipped.
There may be other cases.

For the initial CREATE LIKE statement, It is special,
It derives the subcommand of alter table column.
Just skipping them may be enough.
Instead of skipping subcommands of all statements.
After all, our design is to obtain the actual ddl information from the
catalog instead of parsing raw parsetree.
This is why we cannot skip all subcommands.

Do you have any better ideas?

Regards, Adger.