add If-None-Match and If-Modified-Since

fix https://github.com/chrislusf/seaweedfs/issues/1269

other/java/client/src/main/proto/filer.proto

@@ -123,6 +123,7 @@ message FuseAttributes {
     string user_name = 11; // for hdfs
     repeated string group_name = 12; // for hdfs
     string symlink_target = 13;
+    bytes md5 = 14;
 }
 
 message CreateEntryRequest {