rustdoc doesn't render argument names of reexported FFI functions

[huonw]

E.g. http://doc.rust-lang.org/nightly/std/intrinsics/fn.volatile_set_memory.html

 pub unsafe fn volatile_set_memory<T>(*mut T, u8, usize)

vs. http://doc.rust-lang.org/nightly/core/intrinsics/fn.volatile_set_memory.html

pub unsafe fn volatile_set_memory<T>(dst: *mut T, val: u8, count: usize)

The docs refer to parameters by name, so this functionality is useful.

[tomjakubowski]

I think it's a metadata problem; encode_method_argument_names isn't ever called from encode_info_for_foreign_item.