Assets compiler update + tests

I've updated :
- Less to 1.3.3
- RequireJS to 2.1.3
- Coffe script to 1.4.0

i've also started to write some tests for theses compilers, for now coffe script only

While writing tests i noticed that CoffeescriptCompiler does not work when called by several threads (easy to reproduce with my tests and previous implementation) .

I added a fix for that too, but it can be a sort of performance regression (js context is created/destroyed on demand). I have not found a way to fix that problem while keeping context created once, any ideas welcome.

Finally i added a try catch finally behavior to ensure that rhino context is destroyed (accordingly to mozilla documentation)

Each commit can be cherry-pick independently if needed.