pgsql: Update entry: < * Allow heap reuse of UPDATEd rows if old and

Log Message:
-----------
Update entry:

< * Allow heap reuse of UPDATEd rows if old and new versions are on the
<   same heap page?
> * Allow heap reuse of UPDATEd rows if no indexed columns are changed,
>   and old and new versions are on the same heap page?
<   This is possible for same-page updates because a single index row
<   can point to both old and new values.
>   While vacuum handles DELETEs fine, updating of non-indexed columns, like
>   counters, are difficult for VACUUM to handle efficiently.  This method
>   is possible for same-page updates because a single index row can be
>   used to point to both old and new values.

Modified Files:
--------------
    pgsql/doc:
        TODO (r1.1897 -> r1.1898)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1897&r2=1.1898)
    pgsql/doc/src/FAQ:
        TODO.html (r1.400 -> r1.401)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html.diff?r1=1.400&r2=1.401)