do not pack200 some jars because of duplicate entries

plug/build.gradle

@@ -79,7 +79,8 @@ task webappConfig {
 task pack {
     doLast {
         if (project.pack200 == "true") {
-            libDir.listFiles().stream().filter( { it.getName().endsWith(".jar") } ).forEach {
+            libDir.listFiles().stream().filter( { it.getName().endsWith(".jar") } ).
+                filter({it.length() > 512*1024}).forEach {
                 println "packing $it"
                 def name = it.toString()
                 println "pack200 --no-gzip ${name}.pack $name".execute().text