Re: describe objects, as in pg_depend

Thanks for the comments. Updated patch attached.

In the process of looking it over again, I noticed that in an
assert-enabled build, it's trivial to crash the server with this
function: just pass a nonzero subobjid with an object class that doesn't
take one. This could be fixed easily by turning the Asserts into
elog(ERROR).

Another problem with this function is that a lot of checks that
currently raise errors with elog(ERROR) are now user-facing. On this
issue one possible answer would be to do nothing; another would be to go
over all those calls and turn them into full-fledged ereports.

--
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
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