MPFR version info

[Patrick Pelissier]

> const char *
> my_mpfr_version ()
> {
>   if (try_bug1 ())
>     return "1.0";
>   if (try_bug2 ())
>     return "1.1";
>   else
>     return mpfr_version ();
> }

 It doesn't work :(
 since we need to link with MPFR which provides "mpfr_version", so
the version number is >= 2.1.0.

 Sincerely,
  Patrick Pelissier