Very simple change to allow the factory to create other implementations of IsoMessage

src/main/java/com/solab/iso8583/IsoMessage.java

@@ -57,7 +57,7 @@ public class IsoMessage {
     }
 
     /** Creates a new message with the specified ISO header. This will be prepended to the message. */
-    IsoMessage(String header) {
+    protected IsoMessage(String header) {
     	isoHeader = header;
     }