pgsql: Allow the syntax CREATE TYPE foo, with no parameters, to permit

Log Message:
-----------
Allow the syntax CREATE TYPE foo, with no parameters, to permit explicit
creation of a shell type.  This allows a less hacky way of dealing with
the mutual dependency between a datatype and its I/O functions: make a
shell type, then make the functions, then define the datatype fully.
We should fix pg_dump to handle things this way, but this commit just deals
with the backend.

Martijn van Oosterhout, with some corrections by Tom Lane.

Modified Files:
--------------
    pgsql/doc/src/sgml/ref:
        create_type.sgml (r1.60 -> r1.61)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_type.sgml.diff?r1=1.60&r2=1.61)
    pgsql/doc/src/sgml:
        xtypes.sgml (r1.25 -> r1.26)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/xtypes.sgml.diff?r1=1.25&r2=1.26)
    pgsql/src/backend/catalog:
        pg_type.c (r1.104 -> r1.105)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/pg_type.c.diff?r1=1.104&r2=1.105)
    pgsql/src/backend/commands:
        typecmds.c (r1.86 -> r1.87)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/typecmds.c.diff?r1=1.86&r2=1.87)
    pgsql/src/backend/parser:
        gram.y (r2.530 -> r2.531)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y.diff?r1=2.530&r2=2.531)
    pgsql/src/backend/utils/adt:
        pseudotypes.c (r1.15 -> r1.16)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/pseudotypes.c.diff?r1=1.15&r2=1.16)
    pgsql/src/include/catalog:
        catversion.h (r1.316 -> r1.317)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h.diff?r1=1.316&r2=1.317)
        pg_operator.h (r1.140 -> r1.141)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_operator.h.diff?r1=1.140&r2=1.141)
        pg_proc.h (r1.398 -> r1.399)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h.diff?r1=1.398&r2=1.399)
    pgsql/src/include/utils:
        builtins.h (r1.274 -> r1.275)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/builtins.h.diff?r1=1.274&r2=1.275)
    pgsql/src/test/regress/expected:
        create_type.out (r1.12 -> r1.13)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/create_type.out.diff?r1=1.12&r2=1.13)
    pgsql/src/test/regress/sql:
        create_type.sql (r1.8 -> r1.9)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/create_type.sql.diff?r1=1.8&r2=1.9)