Merge pull request rust-lang#434 from dgreid/setresuid

Add setresuid/setresgid for linux

Author: alexcrichton

src/unix/notbsd/linux/mod.rs

@@ -714,6 +714,8 @@ extern {
                              riovcnt: ::c_ulong,
                              flags: ::c_ulong) -> isize;
     pub fn reboot(how_to: ::c_int) -> ::c_int;
+    pub fn setresgid(rgid: ::gid_t, egid: ::gid_t, sgid: ::gid_t) -> ::c_int;
+    pub fn setresuid(ruid: ::uid_t, euid: ::uid_t, suid: ::uid_t) -> ::c_int;
 
     // Not available now on Android
     pub fn mkfifoat(dirfd: ::c_int, pathname: *const ::c_char,