Re: create table explicitly mention that unique|primary key constraint will create an

I started looking at this specific item and immediately got the idea to actually document in user-facing (i.e., not system catalogs) what these object categories are in which object types share the schema namespace.  The "Other Object Types" section already in the DDL chapter seems to provide a near-perfect place to put this (not sure I like the word "other" there being my only complaint).  The attached patch replaces Laurenz's v1, leaving the create_table changes as-is but presenting an alternative approach to introducing namespacing when we explain why schemas exist.

David J.