Update to latest Google Closure library & compiler in POM
Update version strings in Google Closure release scripts
Update dependency versions in script/bootstrap

Also factor out repeated version strings as variables.

* Clojure 1.5.1
* data.json 0.2.2
* Google Closure Library 0.0-20130212-95c19e7f0f5f
* Rhino 1_7R3