Fix ALTER TABLE ADD COLUMN to disallow the same column types that are

Fix ALTER TABLE ADD COLUMN to disallow the same column types that are
disallowed by CREATE TABLE (eg, pseudo-types); also disallow these types
from being introduced by the range-function syntax.  While at it, allow
CREATE TABLE to create zero-column tables, per recent pghackers discussion.
I am back-patching this into 7.3 since failure to disallow pseudo-types
is arguably a security hole.