Merge pull request #488 from sullis/disallow-java-lang-Thread

add 'java.lang.Thread' to struts.excludedClasses
diff --git a/core/src/main/resources/struts-default.xml b/core/src/main/resources/struts-default.xml
index 045d453..22d11ae 100644
--- a/core/src/main/resources/struts-default.xml
+++ b/core/src/main/resources/struts-default.xml
@@ -45,6 +45,7 @@
                 java.lang.ClassLoader,
                 java.lang.Shutdown,
                 java.lang.ProcessBuilder,
+                java.lang.Thread,
                 sun.misc.Unsafe,
                 com.opensymphony.xwork2.ActionContext" />