mpf_get_d_2exp ignores sign of input

[paul zimmermann]

       Torbjörn,

>   mpf_get_d_2exp() always returns a non-negative value, even for negative
>   input.  I think this is a bug.
>   
> The function works as documented.  No bug.

I disagree. The fine manual says "D * 2^EXP is the (truncated) OP value",
which is wrong if say OP = -0.5.

And why bother write 0.5<=abs(D)<1 instead of 0.5<=D<1 if D is always >= 0?

Paul