Add debug statement for debug.

It might help to determine why require is sometime not a function.

notebook/static/notebook/js/kernelselector.js

@@ -148,6 +148,14 @@ define([
         
         // load kernel js
         if (ks.resources['kernel.js']) {
+
+            // Debug added for Notebook 4.2, please remove at some point in the
+            // future if the following does not append anymore when kernels
+            // have kernel.js
+            //
+            // > Uncaught (in promise) TypeError: require is not a function
+            // 
+            console.info('Dynamically requiring kernel.js, `require` is ', require);
             require([ks.resources['kernel.js']],
                 function (kernel_mod) {
                     if (kernel_mod && kernel_mod.onload) {