Fix bad grammar.

doc/src/sgml/plpgsql.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.158 2010/08/17 04:37:21 petere Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.159 2010/09/16 14:31:20 tgl Exp $ -->
 
 <chapter id="plpgsql">
   <title><application>PL/pgSQL</application> - <acronym>SQL</acronym> Procedural Language</title>
@@ -1351,7 +1351,7 @@ GET DIAGNOSTICS integer_var = ROW_COUNT;
           </listitem>
           <listitem>
            <para>
-            A <command>RETURN QUERY</command> and <command>RETURN QUERY
+            <command>RETURN QUERY</command> and <command>RETURN QUERY
             EXECUTE</command> statements set <literal>FOUND</literal>
             true if the query returns at least one row, false if no row
             is returned.