Fix used_underscore_binding in rustc_serialize

Author: practicalrs

compiler/rustc_serialize/src/opaque.rs

@@ -437,10 +437,10 @@ impl IntEncodedWithFixedSize {
 implEncodable<FileEncoder>forIntEncodedWithFixedSize{
 #[inline]
 fnencode(&self,e:&mutFileEncoder){
-let_start_pos = e.position();
+letstart_pos = e.position();
  e.write_array(self.0.to_le_bytes());
-let_end_pos = e.position();
-debug_assert_eq!((_end_pos - _start_pos),IntEncodedWithFixedSize::ENCODED_SIZE);
+letend_pos = e.position();
+debug_assert_eq!((end_pos - start_pos),IntEncodedWithFixedSize::ENCODED_SIZE);
 }
 }