try moving pipe2 from notbsd to unix

rust-lang#500

Author: oconnor663

src/unix/mod.rs

@@ -417,6 +417,7 @@ extern {
                link_name = "pause$UNIX2003")]
     pub fn pause() -> ::c_int;
     pub fn pipe(fds: *mut ::c_int) -> ::c_int;
+    pub fn pipe2(fds: *mut ::c_int, flags: ::c_int) -> ::c_int;
     pub fn posix_memalign(memptr: *mut *mut ::c_void,
                       align: ::size_t,
                       size: ::size_t) -> ::c_int;

src/unix/notbsd/mod.rs

@@ -734,7 +734,6 @@ extern {
                       events: *mut epoll_event,
                       maxevents: ::c_int,
                       timeout: ::c_int) -> ::c_int;
-    pub fn pipe2(fds: *mut ::c_int, flags: ::c_int) -> ::c_int;
     pub fn mount(src: *const ::c_char,
                  target: *const ::c_char,
                  fstype: *const ::c_char,