(fix) add an idref missing in the previous commit

Author: tuurma

src/main/xar-resources/data/lucene/lucene.xml

@@ -444,7 +444,7 @@
                     attribute <code>store="no"</code>. The field will still be indexed and
                     available for queries though.</para>
 
-                <para><emphasis role="bold">Importing external modules</emphasis>: as can be seen in the field definition for "author" above, expressions can easily become quite verbose, so writing them into an attribute
+                <para xml:id="external-module"><emphasis role="bold">Importing external modules</emphasis>: as can be seen in the field definition for "author" above, expressions can easily become quite verbose, so writing them into an attribute
                     is not convenient. It is thus also possible to import one or more XQuery modules into the index configuration and use the functions declared
                     in the module:</para>
                 <programlisting language="xml" xlink:href="listings/listing-58.xml"></programlisting>