Update CREATE FUNCTION documentation about argument names.

The 9.2 patch that added argument name support in SQL-language functions
missed updating a parenthetical comment about that in the CREATE FUNCTION
reference page.  Noted by Erwin Brandstetter.

doc/src/sgml/ref/create_function.sgml

@@ -134,8 +134,9 @@ CREATE [ OR REPLACE ] FUNCTION
 
      <listitem>
       <para>
-       The name of an argument. Some languages (currently only PL/pgSQL) let
-       you use the name in the function body.  For other languages the
+       The name of an argument. Some languages (currently only SQL and
+       PL/pgSQL)
+       let you use the name in the function body.  For other languages the
        name of an input argument is just extra documentation, so far as
        the function itself is concerned; but you can use input argument names
        when calling a function to improve readability (see <xref