This adds support for the more or less SQL-conforming USAGE privilege
on types and domains.  The intent is to be able restrict which users
can create dependencies on types, which restricts the way in which
owners can alter types.

reviewed by Yeb Havinga

There is what may actually be a mistake in our markup.  The problem is
in a situation like

<para>
 <command>FOO</command> is ...

there is strictly speaking a line break before "FOO".  In the HTML
output, this does not appear to be a problem, but in the man page
output, this shows up, so you get double blank lines at odd places.

So far, we have attempted to work around this with an XSL hack, but
that causes other problems, such as creating run-ins in places like

<acronym>SQL</acronym> <command>COPY</command>

So fix the problem properly by removing the extra whitespace.  I only
fixed the problems that affect the man page output, not all the
places.

Foreign tables are a core component of SQL/MED.  This commit does
not provide a working SQL/MED infrastructure, because foreign tables
cannot yet be queried.  Support for foreign table scans will need to
be added in a future patch.  However, this patch creates the necessary
system catalog structure, syntax support, and support for ancillary
operations such as COMMENT and SECURITY LABEL.

Shigeru Hanada, heavily revised by Robert Haas

Christoph Berg.

is changed to match the hard-wired default.  This avoids accumulating useless
catalog entries, and also provides a path for dropping the owning role without
using DROP OWNED BY.  Per yesterday's complaint from Jaime Casanova, the
need to use DROP OWNED BY for that is less than obvious, so providing this
alternative method might save some user frustration.

The endterm attribute is mainly useful when the toolchain does not support
automatic link target text generation for a particular situation.  In  the
past, this was required by the man page tools for all reference page links,
but that is no longer the case, and it now actually gets in the way of
proper automatic link text generation.  The only remaining use cases are
currently xrefs to refsects.

the keywords as a consequence of the GRANT ALL patch, so we might as well
use them and make the ALTER commands read more naturally.

the privileges that will be applied to subsequently-created objects.

Such adjustments are always per owning role, and can be restricted to objects
created in particular schemas too.  A notable benefit is that users can
override the traditional default privilege settings, eg, the PUBLIC EXECUTE
privilege traditionally granted by default for functions.

Petr Jelinek