Fix 1**z evaluation if z is infinite

closes #8582
On Fri, Dec 12, 2014 at 10:12:51PM -0800, Christopher Smith wrote:
>    In [1]sympy/core/add.py:
> 
>  > @@ -465,6 +465,24 @@ def _eval_is_algebraic_expr(self, syms):
>  >      _eval_is_commutative = lambda self: _fuzzy_group(
>  >          a.is_commutative for a in self.args)
>  >
>  > +    def _eval_is_infinite(self):
>  > +        is_finite = _fuzzy_group((a.is_finite for a in self.args),
>  > +                                 quick_exit=True)
>  > +        if is_finite:
>  > +            return False
>  > +        ret = None
>  > +        for a in self.args:
>  > +            if a.is_infinite:
>  > +                if ret is None:
>  > +                    ret = True
>  > +                else:
>  > +                    return
> 
>    What does it mean to be infinite?

From the docstring:
    finite
    infinite
        object absolute value is bounded (is value is
        arbitrarily large).  See [7]_, [8]_, [9]_.

> Shouldn't these also be infinite?

Yes, sure.