Add res_init

Author: jonhoo

src/unix/mod.rs

@@ -694,6 +694,7 @@ extern {
                        res: *mut *mut addrinfo) -> ::c_int;
     pub fn freeaddrinfo(res: *mut addrinfo);
     pub fn gai_strerror(errcode: ::c_int) -> *const ::c_char;
+    pub fn res_init() -> ::c_int;
 
     #[cfg_attr(target_os = "netbsd", link_name = "__gmtime_r50")]
     pub fn gmtime_r(time_p: *const time_t, result: *mut tm) -> *mut tm;