Normative: handle awkward rounding behavior

Handle awkward rounding behavior when dealing with currencies and the
value of "maximumFractionDigits" is less than 2.

Fixes: #239

spec/numberformat.html

@@ -30,7 +30,11 @@ <h1>SetNumberFormatDigitOptions ( _intlObj_, _options_, _mnfdDefault_, _mxfdDefa
           1. Set _intlObj_.[[MaximumSignificantDigits]] to _mxsd_.
         1. Else if _mnfd_ is not *undefined* or _mxfd_ is not *undefined*, then
           1. Set _intlObj_.[[RoundingType]] to ~fractionDigits~.
-          1. Let _mnfd_ be ? DefaultNumberOption(_mnfd_, 0, 20, _mnfdDefault_).
+          1. If _mxfd_ is not *undefined*, then
+            1. Let _mnfdActualDefault_ be min( _mxfd_, _mnfdDefault_ ).
+          1. Else,
+            1. Let _mnfdActualDefault_ be _mnfdDefault_.
+          1. Let _mnfd_ be ? DefaultNumberOption(_mnfd_, 0, 20, _mnfdActualDefault_).
           1. Let _mxfdActualDefault_ be max( _mnfd_, _mxfdDefault_ ).
           1. Let _mxfd_ be ? DefaultNumberOption(_mxfd_, _mnfd_, 20, _mxfdActualDefault_).
           1. Set _intlObj_.[[MinimumFractionDigits]] to _mnfd_.