Portably generating infinity and NaN

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    Michael> Will float("NaN") work on these systems? (I don't know.) I
    Michael> guess it probably works on some system that isn't IEEE 754.

My thought was that in configure you could test if strtof("NaN") and
strtof("Inf") worked.  If not, calculate the necessary bit patterns at that
point and use conditional compilation in floatmodule.c to generate them.

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