Move raw bytes handling to Encoder/Decoder.

compiler/rustc_incremental/src/persist/file_format.rs

@@ -15,6 +15,7 @@ use std::io::{self, Read};
 use std::path::Path;
 
 use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
+use rustc_serialize::Encoder;
 
 /// The first few bytes of files generated by incremental compilation.
 const FILE_MAGIC: &[u8] = b"RSIC";