[RFC] Adding unit test for rlibc

We are pulling in rlibc into Zinc (hackndev/zinc#113), but while reading the code, I though it could do with some unit tests.

So I have added some tests here, but seem like there are a few issues... Please see comments with `XXX` and respond if you have any thoughts :+1:
Ah, yes, if you're using macros from `std` (or `core`) you need to import them via a `#[phase]`.

For `len`, it's a trait method so you need to have the traits in scope. (i.e. add a [`use std::collections::Collection`](http://doc.rust-lang.org/master/std/collections/trait.Collection.html) in the module with the tests.)