comment fix

src/libsyntax/fold.rs

@@ -475,7 +475,7 @@ fn noop_fold_decl(d: &Decl_, fld: @ast_fold) -> Option<Decl_> {
 }
 
 // lift a function in ast-thingy X fold -> ast-thingy to a function
-// in (ast-thingy X span X fold) -> (ast-thingy X fold). Basically,
+// in (ast-thingy X span X fold) -> (ast-thingy X span). Basically,
 // carries the span around.
 // It seems strange to me that the call to new_fold doesn't happen
 // here but instead in the impl down below.... probably just an