feature request: toggle decorator on/off

[lb-ronyeh]

thought about something like this.

def add42(fn):
    def wrap(i):
        return fn(i) + 42
    wrap.unwrapped = fn
    return wrap

@add42
def mult3(i):
    return i * 3

mult3(1) # 45
mult3.unwrapped(1) # 3