Add more limited large object trigger example.

Author: bmomjian

doc/src/sgml/lo.sgml

@@ -77,13 +77,8 @@ CREATE TRIGGER t_raster BEFORE UPDATE OR DELETE ON image
    For each column that will contain unique references to large objects,
    create a <literal>BEFORE UPDATE OR DELETE</> trigger, and give the column
    name as the sole trigger argument.  You can also restrict the trigger
-   to only execute on updates to the column with:
-
-<programlisting>
-CREATE TRIGGER t_raster BEFORE UPDATE OF raster OR DELETE ON image
-    FOR EACH ROW EXECUTE PROCEDURE lo_manage(raster);
-</programlisting>
-
+   to only execute on updates to the column by using <literal>BEFORE UPDATE
+   OF</literal> <replaceable class="parameter">column_name</replaceable>.
    If you need multiple <type>lo</>
    columns in the same table, create a separate trigger for each one,
    remembering to give a different name to each trigger on the same table.