Old assumptions: Add explicit facts that positive and negative can be infinite

Without this, nan cannot deduce that it is not positive from the facts
finite=False, infinite=False. In general, we want to be able to deduce that if
something is not real and not infinite then it is not positive, negative,
nonnegative, etc.
Old assumptions: oo and -oo are not real

This should be enough to make other facts False, such as oo.is_algebraic.