Fix grammar

backpatched to 8.1

doc/src/sgml/perform.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.54 2005/11/04 23:14:00 petere Exp $
+$PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.54.2.1 2010/07/26 20:30:07 petere Exp $
 -->
 
  <chapter id="performance-tips">
@@ -912,7 +912,7 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
       <para>
        You can get the effect of disabling foreign keys by using
        the <option>-X disable-triggers</> option &mdash; but realize that
-       that eliminates, rather than just postponing, foreign key
+       that eliminates, rather than just postpones, foreign key
        validation, and so it is possible to insert bad data if you use it.
       </para>
      </footnote>