0.11 pre compat

This changeset introduces the compatibly mappings of various parts of `rust-portaudio` such that it can be compiled with a 0.11-pre version of rustc.  The following changes have been introduced:

- Renaming `Eq` and `Ord` to `PartialEq` and `PartialOrd`, respectively (as of [`1217`](https://github.com/mozilla/rust/issues/12517))
- Renaming `std::cast::transmute` to `std::mem:transmute`.
- Using `Vec<S>` over `~[S]`.  

Since 0.11-pre hasn't been released yet, perhaps it might be wise to not accept this pull request directly into master, but perhaps on a new branch where further developments towards 0.11 can take place?