Allow configuration of uid/gid/detach on processes

This just copies the libuv implementation for libnative which seems reasonable
enough (uid/gid fail on windows).

Closes #12082

src/test/run-pass/issue-10626.rs

@@ -33,7 +33,10 @@ pub fn main () {
         args : &[~"child"],
         env : None,
         cwd : None,
-        io : &[]
+        io : &[],
+        uid: None,
+        gid: None,
+        detach: false,
     };
 
     let mut p = process::Process::new(config).unwrap();

src/test/run-pass/process-detach.rs

@@ -0,0 +1,56 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// ignore-fast
+// ignore-win32
+// ignore-android
+
+// This test ensures that the 'detach' field on processes does the right thing.
+// By detaching the child process, they should be put into a separate process
+// group. We test this by spawning a detached process, then killing our own
+// group with a signal.
+//
+// Note that the first thing we do is put ourselves in our own process group so
+// we don't interfere with other running tests.
+
+use std::libc;
+use std::io::process;
+use std::io::signal::{Listener, Interrupt};
+
+fn main() {
+    unsafe { libc::setsid(); }
+
+    let config = process::ProcessConfig {
+        program : "/bin/sh",
+        args : &[~"-c", ~"read a"],
+        io : &[process::CreatePipe(true, false)],
+        detach: true,
+        .. process::ProcessConfig::new()
+    };
+
+    // we shouldn't die because of an interrupt
+    let mut l = Listener::new();
+    l.register(Interrupt).unwrap();
+
+    // spawn the child
+    let mut p = process::Process::new(config).unwrap();
+
+    // send an interrupt to everyone in our process group
+    unsafe { libc::funcs::posix88::signal::kill(0, libc::SIGINT); }
+
+    // Wait for the child process to die (terminate it's stdin and the read
+    // should fail).
+    drop(p.io[0].take());
+    match p.wait() {
+        process::ExitStatus(..) => {}
+        process::ExitSignal(..) => fail!()
+    }
+}
+