Default choice of float_t

[Paul Eggert]

Joseph Myers wrote:
> typedef double float_t;         /* `float' expressions are evaluated as
>                                     `double'.  */
>
> This is a strange default; normal practice is to evaluate float
> expressions as float

Perhaps this dates back to K&R C, where it was common practice to evaluate float 
expressions as double.  That all went out the window with C89, and I agree with 
your proposal to modernize and simplify this.