[R6RS] (integer? +inf.0) => ? [was: NaNs and infinities]

[dyb at cs.indiana.edu]

I would prefer that integer? and rational? be true for +inf.0 and
-inf.0, but I've already given in on that point.  Unless someone else
complains, I suggest we just go with it.

There remains a question in my mind whether real? should return true
for +inf.0 and -inf.0.  If infinity is real and not rational, then it
must be irrational.  Maybe we should add a separate irrational?
predicate (which returns #f for everything in most implementations)
that is also #f for +inf.0 and -inf.0.

Kent