Warn users when failing to require preboot

lib/preboot/require.js

@@ -19,6 +19,8 @@
       bootable = require(fullpath);
     } catch (ex) { // probably we want to throw an error here and halt the application?
       debug('warning Could not load preboot for %s', fullpath, ex.stack);
+      console.warn('Could not load preboot for %s', fullpath, ex.stack);
+      console.warn('Application startup will continue...');
       return callback();
     }
     bootable(app, options, callback);