THRIFT-4566: Pass message to rethrow exception (#1554)

Client: java
diff --git a/lib/java/src/org/apache/thrift/ProcessFunction.java b/lib/java/src/org/apache/thrift/ProcessFunction.java
index be76aff..e6213df 100644
--- a/lib/java/src/org/apache/thrift/ProcessFunction.java
+++ b/lib/java/src/org/apache/thrift/ProcessFunction.java
@@ -45,7 +45,7 @@
       msgType = TMessageType.EXCEPTION;
     } catch (Exception ex) {
       LOGGER.error("Internal error processing " + getMethodName(), ex);
-      if(rethrowUnhandledExceptions()) throw new RuntimeException(ex);
+      if(rethrowUnhandledExceptions()) throw new RuntimeException(ex.getMessage(), ex);
       if(!isOneway()) {
         result = new TApplicationException(TApplicationException.INTERNAL_ERROR,
             "Internal error processing " + getMethodName());