Fix dojo._toArray to enhance performance.

[Tom Trenka]

Change dojo._toArray from this:

	var arr = startWith||[];
	for(var x = offset || 0; x < obj.length; x++){
		arr.push(obj[x]);
	}
	return arr; // Array

to this:

    return (startWith||[]).concat(Array.prototype.slice.call(obj, offset||0));	//	Array

(I figure this is easier than attaching a patch.)

After testing and suggestions from pottedmeat, it turns out that using Array.prototype.slice.call gives a 66% - 100% performance improvement over iterating.

I can commit this, would like a peer review. Passes the unit tests no problem.

[alex]

(In [14289]) merging performance patch from Tom to speed up _toArray calculations (which many NodeList? operations spend much time in). Fixes #6722. !strict