pgsql: Backpatch FAQ entry for null concatenation.

Log Message:
-----------
Backpatch FAQ entry for null concatenation.

Tags:
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REL8_2_STABLE

Modified Files:
--------------
    pgsql/doc:
        FAQ (r1.402.2.1 -> r1.402.2.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/FAQ.diff?r1=1.402.2.1&r2=1.402.2.2)
        FAQ_AIX (r1.19 -> r1.19.2.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/FAQ_AIX.diff?r1=1.19&r2=1.19.2.1)
        FAQ_HPUX (r1.14 -> r1.14.2.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/FAQ_HPUX.diff?r1=1.14&r2=1.14.2.1)
        FAQ_IRIX (r1.3 -> r1.3.12.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/FAQ_IRIX.diff?r1=1.3&r2=1.3.12.1)
        FAQ_MINGW (r1.5 -> r1.5.2.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/FAQ_MINGW.diff?r1=1.5&r2=1.5.2.1)
        FAQ_SCO (r1.11 -> r1.11.8.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/FAQ_SCO.diff?r1=1.11&r2=1.11.8.1)
        FAQ_Solaris (r1.22.2.1 -> r1.22.2.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/FAQ_Solaris.diff?r1=1.22.2.1&r2=1.22.2.2)
    pgsql/doc/src/FAQ:
        FAQ.html (r1.358.2.1 -> r1.358.2.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/FAQ.html.diff?r1=1.358.2.1&r2=1.358.2.2)
    pgsql/doc/src/sgml/ref:
        psql-ref.sgml (r1.175.2.2 -> r1.175.2.3)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/psql-ref.sgml.diff?r1=1.175.2.2&r2=1.175.2.3)