function indexed( x, start, end, fcn, thisArg ) {
	var i;
	for ( i = start; i < end; i++ ) {
		x[ i ] = fcn.call( thisArg, x[ i ], i, x );
	}
	return x;
}
Fills all elements within a portion of an indexed array according to a callback function.

@private
@param {Collection} x - input array
@param {integer} start - starting index (inclusive)
@param {integer} end - ending index (exclusive)
@param {Function} fcn - callback function
@param {*} thisArg - callback function execution context
@returns {Array} output array

@example
function fcn() {
    return 5;
}

var x = [ 1, 2, 3, 4 ];

var out = indexed( x, 1, 3, fcn, {} );
// returns [ 1, 5, 5, 4 ]