temp

<concat destfile="temp.xml" >
 <fileset dir="." includes="**/*.txt" />
</concat>
<replace file="temp.xml">
 <replacetoken><![CDATA[<xml? encoding="UTF-8" />]]></replacetoken>
 <replacevalue></replacevalue>
</replace>
<concat destfile="summary.xml" >
 <fileset file=".txt" />
 <fileset file="temp.xml" />
</concat>