- Move io, run and rand to core.
- Remove incorrect ctypes module (use libc).
- Remove os-specific modules for os and fs.
- Split fs between core::path and core::os.
Now that core exports "option" as a synonym for option::t, search-and-
replace option::t with option.
The only place that still refers to option::t are the modules in libcore
that use option, because fixing this requires a new snapshot
(forthcoming).
Patrick Walton