Introduce fn@ as a synonym for fn

Author: brson

src/comp/syntax/parse/parser.rs

@@ -2147,6 +2147,9 @@ fn parse_fn_proto(p: parser) -> ast::proto {
     if p.peek() == token::POUND {
         p.bump();
         ast::proto_bare
+    } else if p.peek() == token::AT {
+        p.bump();
+        ast::proto_fn
     } else {
         ast::proto_fn
     }