If none of you is working on it right now, I'll produce a new patch.
Mark, how about this:

     def __add__(self, other, context=None, raiseit=False):
        """Returns self + other.

        -INF + INF (or the reverse) cause InvalidOperation errors.
        """
        other = _convert_other(other, raiseit)
        if other is NotImplemented:
            return other


Then the context functions could look cleaner.