Allow debugging errors in server gen js
Allow debugging errors in server gen js

This change prints a useful message and outputs the file with the issue.

shakacode/react_on_rails,szyablitsky/react_on_rails,shakacode/react_on_rails,shakacode/react_on_rails,szyablitsky/react_on_rails,shakacode/react_on_rails,szyablitsky/react_on_rails,shakacode/react_on_rails,szyablitsky/react_on_rails