function _checkForMethod(methodname, fn) {
    return function () {
      var length = arguments.length;
      if (length === 0) {
        return fn();
      }
      var obj = arguments[length - 1];
      return _isArray(obj) || typeof obj[methodname] !== 'function' ? fn.apply(this, arguments) : obj[methodname].apply(obj, Array.prototype.slice.call(arguments, 0, length - 1));
    };
  }
This checks whether a function has a [methodname] function. If it isn't an
array it will execute that function otherwise it will default to the ramda
implementation.

@private
@param {Function} fn ramda implementation
@param {String} methodname property to check for a custom implementation
@return {Object} Whatever the return value of the method is.