std::os::pipe doesn't handle error correctly

[hannobraun]

The function std::os::pipe just fails if the call to libc::pipe returns an error code.

This can be easily triggered with the following program:

use std::io::Command;

fn main() {
    let mut p = Vec::new();

    loop {
        match Command::new("cat").spawn() {
            Ok(process) =>
                p.push(process),
            Err(error) =>
                fail!("Error: {}", error)
        }

        print!("{}\n", p.len());
    }
}

On my machine (Ubuntu 14.04, x86_64), the program fails at 338 processes with the following message:

task '<main>' failed at 'assertion failed: `(left == right) && (right == left)` (left: `-1`, right: `0`)', /home/hanno/Projects/vndf/vendor/rust/src/libstd/os.rs:517

I believe that os::pipe() should return a Result (IoResult?) which should be passed up the chain. When I tried implementing this change, however, I quickly ran into trouble with users of the function. While some already return IoResult and can just pass the error up the chain, others don't. I wasn't sure, if I should change even more function signatures or just fail in these cases.

Since this isn't a problem for me currently and my time is very limited, I won't work further on this, sorry!
Maybe someone who understands the requirements of the calling code better might want to take a look.