pgsql: Ensure that all and tags have IDs.

Log Message:
-----------
Ensure that all <sect1> and <refentry> tags have IDs.  This is needed
to ensure that the resulting webpages have predictable URLs, instead of
ever-changing numeric IDs.  The new contrib docs were the biggest
offender, but some old stuff had the problem too.  Also, rename a couple
of new contrib sgml files for consistency's sake.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        adminpack.sgml (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/adminpack.sgml?r1=1.1&r2=1.2)
        btree-gist.sgml (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/btree-gist.sgml?r1=1.1&r2=1.2)
        contrib.sgml (r1.5 -> r1.6)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/contrib.sgml?r1=1.5&r2=1.6)
        datetime.sgml (r2.56 -> r2.57)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datetime.sgml?r1=2.56&r2=2.57)
        dblink.sgml (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/dblink.sgml?r1=1.1&r2=1.2)
        filelist.sgml (r1.54 -> r1.55)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/filelist.sgml?r1=1.54&r2=1.55)
        install-win32.sgml (r1.42 -> r1.43)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/install-win32.sgml?r1=1.42&r2=1.43)

Added Files:
-----------
    pgsql/doc/src/sgml:
        pgbuffercache.sgml (r2.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/pgbuffercache.sgml?rev=2.1&content-type=text/x-cvsweb-markup)
        pgfreespacemap.sgml (r2.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/pgfreespacemap.sgml?rev=2.1&content-type=text/x-cvsweb-markup)
        pgstandby.sgml (r2.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/pgstandby.sgml?rev=2.1&content-type=text/x-cvsweb-markup)
        pgtrgm.sgml (r2.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/pgtrgm.sgml?rev=2.1&content-type=text/x-cvsweb-markup)

Removed Files:
-------------
    pgsql/doc/src/sgml:
        buffercache.sgml
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/buffercache.sgml)
        freespacemap.sgml
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/freespacemap.sgml)
        standby.sgml
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/standby.sgml)
        trgm.sgml
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/trgm.sgml)