adding the junit jars to the source distribution, problem reported by Michael Durket

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@1583518 13f79535-47bb-0310-9956-ffa450edef68

build.xml

@@ -1080,8 +1080,7 @@
 
     <copy todir="${src.dist.lib}">
       <fileset dir="${lib.dir}">
-        <include name="*.jar"/>
-        <include name="*.zip"/>
+        <include name="optional/junit*.jar"/>
         <include name="README"/>
         <include name="libraries.properties"/>
       </fileset>