pgsql: Require superuser privilege to create base types (but not

Log Message:
-----------
Require superuser privilege to create base types (but not composites, enums,
or domains). This was already effectively required because you had to own
the I/O functions, and the I/O functions pretty much have to be written in
C since we don't let PL functions take or return cstring. But given the
possible security consequences of a malicious type definition, it seems
prudent to enforce superuser requirement directly. Per recent discussion.

Modified Files:
--------------
pgsql/doc/src/sgml/ref:
create_type.sgml (r1.76 -> r1.77)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_type.sgml?r1=1.76&r2=1.77)
pgsql/src/backend/commands:
typecmds.c (r1.121 -> r1.122)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/typecmds.c?r1=1.121&r2=1.122)