Optimise $tw.utils.parseStringArray()

On my machine, the following test performed on the prerelease improves
from 40ms to 8ms with this patch:

```
var a =
$tw.utils.stringifyList($tw.wiki.allTitles());console.time();$tw.utils.p
arseStringArray(a);console.timeEnd()
```

boot/boot.js

@@ -271,14 +271,15 @@ $tw.utils.stringifyList = function(value) {
 $tw.utils.parseStringArray = function(value) {
 	if(typeof value === "string") {
 		var memberRegExp = /(?:^|[^\S\xA0])(?:\[\[(.*?)\]\])(?=[^\S\xA0]|$)|([\S\xA0]+)/mg,
-			results = [],
+			results = [], names = {},
 			match;
 		do {
 			match = memberRegExp.exec(value);
 			if(match) {
 				var item = match[1] || match[2];
-				if(item !== undefined && results.indexOf(item) === -1) {
+				if(item !== undefined && !$tw.utils.hop(names,item)) {
 					results.push(item);
+					names[item] = true;
 				}
 			}
 		} while(match);