fix mojom bindings generator exception error message

mojo/public/tools/bindings/mojom_bindings_generator.py

 #!/usr/bin/env python
 # Copyright 2013 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.
 
 """The frontend for the Mojo bindings system."""
 
 
 import argparse
 import imp
@@ skipping 178 matching lines @@
 
     if rel_filename.path in imported_filename_stack:
       print "%s: Error: Circular dependency" % rel_filename.path + \
           MakeImportStackMessage(imported_filename_stack + [rel_filename.path])
       sys.exit(1)
 
     try:
       with open(rel_filename.path) as f:
         source = f.read()
     except IOError as e:
-      print "%s: Error: %s" % (e.rel_filename.path, e.strerror) + \
+      print "%s: Error: %s" % (rel_filename.path, e.strerror) + \
           MakeImportStackMessage(imported_filename_stack + [rel_filename.path])
       sys.exit(1)
 
     try:
       tree = Parse(source, rel_filename.path)
     except Error as e:
       full_stack = imported_filename_stack + [rel_filename.path]
       print str(e) + MakeImportStackMessage(full_stack)
       sys.exit(1)
 
@@ skipping 100 matching lines @@
       "-o", "--output_dir", dest="output_dir", default=".",
       help="output directory for precompiled templates")
   precompile_parser.set_defaults(func=_Precompile)
 
   args, remaining_args = parser.parse_known_args()
   return args.func(args, remaining_args)
 
 
 if __name__ == "__main__":
   sys.exit(main())