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Please critique this tail call optimizing decorator I've written. I've
tried to fix the pitfalls of other proposed decorators, and the result
is this one that supports mutual recursion, does not use exceptions,
stack inspection or any implementation-dependent hack, and is pretty
short and fast - the fastest out of the ones I could find and try. In
fact, in tail-recursive environments I tested the impact of using the
decorator is difficult to even measure, as the extra time the
decorator takes to run is probably saved by the better use of cache
memory. The only caveat is that if used in a function that's not
called in a tail-recursive fashion, bad things will happen.