librustc: De-@mut the span handler

src/libsyntax/attr.rs

@@ -355,8 +355,7 @@ pub fn find_stability<AM: AttrMetaMethods, It: Iterator<AM>>(mut metas: It) -> O
     None
 }
 
-pub fn require_unique_names(diagnostic: @mut SpanHandler,
-                            metas: &[@MetaItem]) {
+pub fn require_unique_names(diagnostic: @SpanHandler, metas: &[@MetaItem]) {
     let mut set = HashSet::new();
     for meta in metas.iter() {
         let name = meta.name();
@@ -381,7 +380,7 @@ pub fn require_unique_names(diagnostic: @mut SpanHandler,
  * present (before fields, if any) with that type; reprensentation
  * optimizations which would remove it will not be done.
  */
-pub fn find_repr_attr(diagnostic: @mut SpanHandler, attr: @ast::MetaItem, acc: ReprAttr)
+pub fn find_repr_attr(diagnostic: @SpanHandler, attr: @ast::MetaItem, acc: ReprAttr)
     -> ReprAttr {
     let mut acc = acc;
     match attr.node {