Auto merge of #453 - nix-rust:asomers-kevent, r=posborne

Asomers kevent

This is a rebase of @asomers work on master to resolve a merge conflict so we can get things merged up.

Author: homu

CHANGELOG.md

@@ -20,6 +20,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Changed
 - The minimum supported version of rustc is now 1.7.0.
   ([#444](https://github.com/nix-rust/nix/pull/444))
+- Implement `Send` for `KEvent`
+  ([#442](https://github.com/nix-rust/nix/pull/442))
 - Changed `KEvent` to an opaque structure that may only be modified by its
   constructor and the `ev_set` method.
   ([#415](https://github.com/nix-rust/nix/pull/415))

src/sys/event.rs

@@ -191,6 +191,13 @@ pub fn kqueue() -> Result<RawFd> {
     Errno::result(res)
 }
 
+
+// KEvent can't derive Send because on some operating systems, udata is defined
+// as a void*.  However, KEvent's public API always treats udata as a uintptr_t,
+// which is safe to Send.
+unsafe impl Send for KEvent {
+}
+
 impl KEvent {
     pub fn new(ident: uintptr_t, filter: EventFilter, flags: EventFlag,
                fflags:FilterFlag, data: intptr_t, udata: uintptr_t) -> KEvent {