function extend( arr, ext ) {
	var i;
	for ( i = 0; i < ext.length; i++ ) {
		arr.push( ext[ i ] );
	}
	return arr;
}
Extends an array by the elements of another array.

@private
@param {Array} arr - input array
@param {Array} ext - array to extend `arr` with
@returns {Array} mutated input array

@example
var arr = [ 1, 2, 3 ];
var out = extend( arr, [ 4, 5 ] );
// returns [ 1, 2, 3, 4, 5 ]