Add WUNTRACED

Cargo.toml

 [package]
 name = "redox_syscall"
-version = "0.1.33"
+version = "0.1.34"
 description = "A Rust library to access raw Redox system calls"
 license = "MIT"
 authors = ["Jeremy Soller <jackpot51@gmail.com>"]

src/flag.rs

@@ -104,3 +104,4 @@ pub const SA_NODEFER: usize =   0x40000000;
 pub const SA_RESETHAND: usize = 0x80000000;
 
 pub const WNOHANG: usize = 1;
+pub const WUNTRACED: usize = 2;