Integrate the operator class section into the comprehensive extending SQL

chapter as well.

doc/src/sgml/extend.sgml

 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/extend.sgml,v 1.21 2003/04/10 01:22:44 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/extend.sgml,v 1.22 2003/04/13 09:57:35 petere Exp $
 -->
 
  <chapter id="extend">
@@ -106,6 +106,7 @@ $Header: /cvsroot/pgsql/doc/src/sgml/extend.sgml,v 1.21 2003/04/10 01:22:44 pete
   &xtypes;
   &xoper;
   &xaggr;
+  &xindex;
 
  </chapter>
 

doc/src/sgml/postgres.sgml

 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/postgres.sgml,v 1.50 2003/04/10 01:22:44 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/postgres.sgml,v 1.51 2003/04/13 09:57:35 petere Exp $
 -->
 
 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V3.1//EN" [
@@ -211,7 +211,6 @@ $Header: /cvsroot/pgsql/doc/src/sgml/postgres.sgml,v 1.50 2003/04/10 01:22:44 pe
   </partintro>
 
   &extend;
-  &xindex;
   &indexcost;
   &rules;
   &trigger;