function XTakeWhile(f, xf) {
    this.xf = xf;
    this.f = f;
  }
Returns a new list containing the last `n` elements of a given list, passing
each value to the supplied predicate function, and terminating when the
predicate function returns `false`. Excludes the element that caused the
predicate function to fail. The predicate function is passed one argument:
*(value)*.

@func
@memberOf R
@since v0.16.0
@category List
@sig (a -> Boolean) -> [a] -> [a]
@sig (a -> Boolean) -> String -> String
@param {Function} fn The function called per iteration.
@param {Array} xs The collection to iterate over.
@return {Array} A new array.
@see R.dropLastWhile, R.addIndex
@example

     const isNotOne = x => x !== 1;

     R.takeLastWhile(isNotOne, [1, 2, 3, 4]); //=> [2, 3, 4]

     R.takeLastWhile(x => x !== 'R' , 'Ramda'); //=> 'amda'