Fix incorrectly resolved conflict, and add error message for missing sources.

ppapi/generators/idl_generator.py

-#!/usr/bin/python
-#
+#!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import sys
 
 from idl_log import ErrOut, InfoOut, WarnOut
 from idl_option import GetOption, Option, ParseOptions
 from idl_parser import ParseFiles
 
@@ skipping 247 matching lines @@
   filenames = ParseOptions(args)
   ast = ParseFiles(filenames)
 
   return Generator.Run(ast)
 
 
 if __name__ == '__main__':
   GeneratorReleaseTest('Test Gen', 'testgen', 'Generator Class Test.')
   sys.exit(Main(sys.argv[1:]))