[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:
The errors where simply that `assert!` (and friends) are not defined.
Turns out that it's not enough to add `#[cfg(test)] extern crate test;`, which seemed like an obvious way of fixing this... 

Following your advise I checked `libcollections/lib.rs` and adding `#[cfg(test)] #[phase(plugin, link)] extern crate std;` for some reason fixes this. This still looks like a little issue in the compiler, don't you think?