function intersect( a, b ) {
	var out;
	var i;

	out = [];
	for ( i = 0; i < a.length; i++ ) {
		if ( contains( b, a[ i ] ) ) {
			out.push( a[ i ] );
		}
	}
	return out;
}
Returns an array of elements that are common to both input arrays.

@private
@param {Array} a - first array
@param {Array} b - second array
@returns {Array} intersection array