fix cachePartials extension name

[lavaxun]

fix multi-dotted extension name usage for partials in meanjs

{
...
extname: '.server.view.html'
...
}

[ErisDS]

@axnux sorry for the very slow reply.

Could you explain in a little more detail what this patch fixes? It would also be fantastic if you could add a test to demonstrate what is fixed as a result.