pgsql: Update timezone documentation to reflect current reality: instead

Log Message:
-----------
Update timezone documentation to reflect current reality: instead of
giving tables of known timezone names, refer the user to the system views.
Joachim Wieland

Modified Files:
--------------
    pgsql/doc/src/sgml:
        datatype.sgml (r1.175 -> r1.176)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datatype.sgml.diff?r1=1.175&r2=1.176)
        datetime.sgml (r2.52 -> r2.53)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datetime.sgml.diff?r1=2.52&r2=2.53)
        func.sgml (r1.339 -> r1.340)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml.diff?r1=1.339&r2=1.340)
    pgsql/doc/src/sgml/ref:
        set.sgml (r1.89 -> r1.90)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/set.sgml.diff?r1=1.89&r2=1.90)