Fix to_date() and to_timestamp() to handle year masks of length < 4 so

they wrap toward year 2020, rather than the inconsistent behavior we had
before.

doc/src/sgml/func.sgml

@@ -5548,6 +5548,15 @@ SELECT SUBSTRING('XY1234Z', 'Y*?([0-9]{1,3})');
       </para>
      </listitem>
 
+     <listitem>
+      <para>
+       If the year format specification is less than four digits, e.g.
+       <literal>YYY</>, and the supplied year is less than four digits,
+       the year will be adjusted to be nearest to the year 2020, e.g.
+       <literal>95</> becomes 1995.
+      </para>
+     </listitem>
+
      <listitem>
       <para>
        The <literal>YYYY</literal> conversion from string to <type>timestamp</type> or