fix(cmn): use bytes=... when sending as well

Previously, `bytes=` was just parsed, but not sent to the server.
This change is motivated by a similar change in this commit:
http://goo.gl/AvyvLb

Author: Byron

src/rust/api/cmn.rs

@@ -440,7 +440,7 @@ impl Header for ContentRange {
 
 impl HeaderFormat for ContentRange {
     fn fmt_header(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-        try!(fmt.write_str("bytes "));
+        try!(fmt.write_str("bytes="));
         match self.range {
             Some(ref c) => try!(c.fmt(fmt)),
             None => try!(fmt.write_str("*"))

src/rust/lib.rs

@@ -129,9 +129,9 @@ bar\r\n\
     #[test]
     fn content_range() {
         for &(ref c, ref expected) in 
-          &[(ContentRange {range: None, total_length: 50 }, "Content-Range: bytes */50\r\n"),
+          &[(ContentRange {range: None, total_length: 50 }, "Content-Range: bytes=*/50\r\n"),
             (ContentRange {range: Some(Chunk { first: 23, last: 40 }), total_length: 45},
-             "Content-Range: bytes 23-40/45\r\n")] {
+             "Content-Range: bytes=23-40/45\r\n")] {
             let mut headers = hyper::header::Headers::new();
             headers.set(c.clone());
             assert_eq!(headers.to_string(), expected.to_string());