lib: change == to === in linkedlist

Also removed a TODO comment that is no longer viable and left a note
about the potentially confusing property naming convention for future
readers.

PR-URL: https://github.com/nodejs/node/pull/9362
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Bryan English <bryan@bryanenglish.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>

lib/internal/linkedlist.js

@@ -16,7 +16,7 @@ exports.create = create;
 
 // show the most idle item
 function peek(list) {
-  if (list._idlePrev == list) return null;
+  if (list._idlePrev === list) return null;
   return list._idlePrev;
 }
 exports.peek = peek;
@@ -54,7 +54,7 @@ function append(list, item) {
   }
 
   // items are linked  with _idleNext -> (older) and _idlePrev -> (newer)
-  // TODO: swap the linkage to match the intuitive older items at "prev"
+  // Note: This linkage (next being older) may seem counter-intuitive at first.
   item._idleNext = list._idleNext;
   item._idlePrev = list;