Comment 3 for bug 241117

There has been another request for similar functionality: https://bugs.launchpad.net/pycrypto/+bug/1014715

As I mentioned there, this could be useful for implementing disk encryption modes of operation (e.g. ESSIV, XTS, etc.). I'm not sure what the API should look like yet, but I think it would be good if we had an API that allowed a cipher to be reinitialized with the same key without necessarily running the key-scheduling algorithm again.