Doc: update section 9.13 for new function table layout.

This includes the usual amount of editorial cleanup, such as
correcting wrong or less-helpful-than-they-could-be examples.

I moved the two tsvector-updating triggers into "9.28 Trigger
Functions", which seems like a better home for them.  (I believe
that section didn't exist when this text was originally written.)

doc/src/sgml/textsearch.sgml

@@ -1705,10 +1705,15 @@ SELECT numnode('foo & bar'::tsquery);
        or only negated terms.  For example:
 
 <screen>
+SELECT querytree(to_tsquery('defined'));
+ querytree
+-----------
+ 'defin'
+
 SELECT querytree(to_tsquery('!defined'));
  querytree
 -----------
-
+ T
 </screen>
       </para>
      </listitem>