Added "listReverse" function.

Was inspired by an article about jobinterviews, telling that 19 of 20 candidates
failed to come up with a function to reverse a singly linked list..
I thought up this way of doing it with recursion, seems easy, maybe
I misunderstood the question, but anyhow, I figure it's neat to have a function to
do that.. Not that I need it right now, but who knows, maybe in the future.. BLOAT! ;)