Remove by-mutable-ref mode from the compiler

and test cases. Closes #3513

src/libsyntax/parse/parser.rs

@@ -20,13 +20,13 @@ use obsolete::{
     ObsoleteLowerCaseKindBounds, ObsoleteLet,
     ObsoleteFieldTerminator, ObsoleteStructCtor,
     ObsoleteWith, ObsoleteClassMethod, ObsoleteClassTraits,
-    ObsoleteModeInFnType
+    ObsoleteModeInFnType, ObsoleteByMutRefMode
 };
 use ast::{_mod, add, alt_check, alt_exhaustive, arg, arm, attribute,
              bind_by_ref, bind_by_implicit_ref, bind_by_value, bind_by_move,
              bitand, bitor, bitxor, blk, blk_check_mode, bound_const,
              bound_copy, bound_send, bound_trait, bound_owned, box, by_copy,
-             by_move, by_mutbl_ref, by_ref, by_val, capture_clause,
+             by_move, by_ref, by_val, capture_clause,
              capture_item, cdir_dir_mod, cdir_src_mod, cdir_view_item,
              class_immutable, class_mutable,
              crate, crate_cfg, crate_directive, decl, decl_item, decl_local,
@@ -570,9 +570,10 @@ impl parser {
 
     fn parse_arg_mode() -> mode {
         if self.eat(token::BINOP(token::AND)) {
-            self.span_fatal(copy self.last_span,
-                            ~"Obsolete syntax has no effect");
-            expl(by_mutbl_ref)
+            self.obsolete(copy self.span,
+                          ObsoleteByMutRefMode);
+            // Bogus mode, but doesn't matter since it's an error
+            expl(by_ref)
         } else if self.eat(token::BINOP(token::MINUS)) {
             expl(by_move)
         } else if self.eat(token::ANDAND) {