repl: dynamically lookup the require extensions for tab complete

Removes 2 TODO items

lib/repl.js

@@ -454,11 +454,7 @@ REPLServer.prototype.complete = function(line, callback) {
     completionGroupsLoaded();
   } else if (match = line.match(requireRE)) {
     // require('...<Tab>')
-    //TODO: suggest require.exts be exposed to be introspec registered
-    //extensions?
-    //TODO: suggest include the '.' in exts in internal repr: parity with
-    //`path.extname`.
-    var exts = ['.js', '.node'];
+    var exts = Object.keys(require.extensions);
     var indexRe = new RegExp('^index(' + exts.map(regexpEscape).join('|') +
                              ')$');