But, as far as I can tell, I assure that the modifications I have performed are completely compatible with the Standard Ethernet. You can take a look at the README.txt file included in the tar.gz attachment and you can see that the only modifications I have performed is to make both the timeout and the response timeout for DHCP request parametrizable from the Arduino sketch. I have not included a new library, because I think it is more appropriate to adapt the Ethernet library to make those timeouts configurable from the Arduino sketch.
I have found it comfortable, because, when doing some tests, I realized that the default timeout is, in my humble opinion, a bit high (60 seconds). Of course, it is completely backward compatible, because if you do not specify any timeout, you will have exactly the same behaviour as we have now.
If you prefer, see Ethernet.hpp and Ethernet.cpp files to see my modifications (compare them with the same files you have in your Arduino environment).
I think it could be useful for other developers.
Thanks for your time 
BR.