[R6RS] Predicate for "neither infinite nor NaN"

[dyb at cs.indiana.edu]

> The specification of arithmetic in a number of places refers to
> numbers that can be anything except infinite or NaN.  Should we have a
> predicate for this?  (Jaffer's SRFI has `finite?' for this purpose, I
> believe.)

Such a predicate might be nice.  The name finite? is okay with me.  We
already have a nan? predicate, right?  Will we also have an infinite? 
predicate, so that the predicates finite?, infinite?, and nan? are
orthogonal and cover the space of all real numbers?

Kent