auto merge of #16291 : nham/rust/byte_literals, r=alexcrichton

This replaces many instances chars being casted to u8 with byte literals.

src/libstd/os.rs

@@ -293,7 +293,7 @@ pub fn env_as_bytes() -> Vec<(Vec<u8>,Vec<u8>)> {
         fn env_convert(input: Vec<Vec<u8>>) -> Vec<(Vec<u8>, Vec<u8>)> {
             let mut pairs = Vec::new();
             for p in input.iter() {
-                let mut it = p.as_slice().splitn(1, |b| *b == '=' as u8);
+                let mut it = p.as_slice().splitn(1, |b| *b == b'=');
                 let key = Vec::from_slice(it.next().unwrap());
                 let val = Vec::from_slice(it.next().unwrap_or(&[]));
                 pairs.push((key, val));