auto merge of #8666 : nikomatsakis/rust/issue-3678-extern-fn-types, r=pcwalton

Change the type of crust fns like this one:

    extern fn foo() { ... }

from `*u8` to `extern "C" fn()`.

r? @pcwalton (or whomever)

diff --cc src/librustc/middle/trans/base.rs
Simple merge

diff --cc src/librustc/middle/typeck/collect.rs
Simple merge