message: rational: check for NaN when approximating floats
  We had a test for NaN already, but thanks to undefined casts it
  was only passing by luck -- on armv7hl it failed:
  Now we check for NaN explicitly.
diff: @@ -774,7 +774,7 @@ fn approximate_float_unsigned<T, F>(val: F, max_error: F, max_iterations: usize)
  // Continued fractions algorithm
  // http://mathforum.org/dr.math/faq/faq.fractions.html#decfrac
  - if val < F::zero() {
  + if val < F::zero() || val.is_nan() {
  return None;
  }
  