Make "use" statements shadow "extern mod" and require "extern mod" to come first

[dpc]

See the following example:

[mutex:rust/rg]% cat main.rs
extern mod sdl;

use core::io;
use sdl::sdl;
use sdl::video;
use sdl::video::{DoubleBuf, HWSurface, Surface};

fn main() {
    io::print("Hi!\n");
    sdl::init(&[sdl::sdl::InitEverything]);
    video::set_video_mode(640,480,32,&[],&[sdl::video::DoubleBuf]);

    while !io::stdin().eof() {
        io::print("Hi!\n");
    }
}
[mutex:rust/rg]% make       
rustc -o rg main.rs
main.rs:10:1: 10:10 error: unresolved name: sdl::init
main.rs:10  sdl::init(&[sdl::sdl::InitEverything]);
            ^~~~~~~~~
error: aborting due to previous error
make: *** [rg] Błąd 101

The video::set_video_mode works just fine, but sdl::init does not.

[catamorphism]

If nothing else, the error message should be better. (I would expect that you'd get an error about the ambiguity of sdl, as in the crate sdl, and sdl, as imported with use sdl::sdl;)

[pcwalton]

Edited title to the solution I think we should choose to this.

[catamorphism]

Not a blocker for 0.6, de-milestoning.

[metajack]

Is this what is causing things like this to fail?

extern mod core_foundation;
use core_foundation;

The fix is easy (just remove the unnecessary use) but I thought I'd ask just in case.

[catamorphism]

This is done.