DUBBO-791 转换成高层异常时，加上高层的信息

git-svn-id: http://code.alibabatech.com/svn/dubbo/trunk@221 1a56cb94-b969-4eaa-88fa-be21384802f2

dubbo-rpc-default/src/main/java/com/alibaba/dubbo/rpc/protocol/dubbo/DubboProtocol.java

@@ -295,9 +295,9 @@ public class DubboProtocol extends AbstractProtocol {
         }
         try {
             return Exchangers.connect(url ,requestHandler);
-            
         } catch (RemotingException e) {
-            throw new RpcException(e.getMessage(), e);
+            throw new RpcException("Fail to create remoting client for service(" + url
+            		+ "):" + e.getMessage(), e);
         }
     }