psql: \d+ shows OID-ness

This patch makes psql's \d+ command indicate whether the table in
question contains OIDs or not. I didn't add this information to \d, on
the grounds that \d is more commonly used and few people will care
whether the table as OIDs. Example output:

nconway=# create table t1 () with oids;
CREATE TABLE
nconway=# create table t2 () without oids;
CREATE TABLE
nconway=# \d+ t1
Table "public.t1"
Column | Type | Modifiers | Description
--------+------+-----------+-------------
Contains OIDs: yes

nconway=# \d+ t2
Table "public.t2"
Column | Type | Modifiers | Description
--------+------+-----------+-------------
Contains OIDs: no

I also fixed a bunch of markup in the psql reference manual (which takes
up about 90% of the patch itself).

Barring any objections I'll apply this patch within 24 hours.

-Neil