Upgrade closure-library version

Upgrade the closure-library version and always use the native json function 

build size:

master branch:
```
2014-08-07 17:18:56,478 build/ol.js: node tasks/build.js buildcfg/ol.json build/ol.js
info ol Parsing dependencies
info ol Compiling 327 sources
2014-08-07 17:19:18,502 build/ol.js: uncompressed:   385930 bytes
2014-08-07 17:19:18,502 build/ol.js:   compressed:   116322 bytes, (saved 69.86%)
```
newer-closure-library branch:
```
2014-08-07 17:17:03,833 build/ol.js: node tasks/build.js buildcfg/ol.json build/ol.js
info ol Parsing dependencies
info ol Compiling 330 sources
2014-08-07 17:17:36,710 build/ol.js: uncompressed:   385117 bytes
2014-08-07 17:17:36,711 build/ol.js:   compressed:   115908 bytes, (saved 69.90%)
```