Syntax coloring doesn't work with emacs 23.1.1

What steps will reproduce the problem?
*First Case*
1. install protobuf-mode.el file as indicated in the header
   1. Move the file somewhere in the emacs load-path
   2. Add (require 'protobuf-mode) to .emacs
2. launch emacs

If I change the installation process to the following :

1. install protobuf-mode.el file as indicated in the header, but put this in 
the .emacs :
(autoload 'protobuf-mode "protobuf-mode" "Major mode for editing protobuf 
defitinion." t)
(add-to-list 'auto-mode-alist '("\\.proto$" . protobuf-mode))
2. open some .proto file

What is the expected output? What do you see instead?
first case : 
You get a an error during initialization of emacs :

Warning (initialization): An error occurred while loading `/home/tuleu/.emacs':

error: `c-lang-defconst' must be used in a file

*Second Case*
no coloring of "required" "optional" "repeated" keywords
no coloring of "namespace". For example, the line "package foo.bar.baz" doesn't 
put a special color for "bar" and "baz"

What version of the product are you using? On what operating system?
Protobuf installed through Ubuntu 10.04 packages, and emacs 23.1.1 installed 
through the same distribution

Please provide any additional information below.

Performed the same steps with emacs 22 : the syntax coloring is working fine, 
both installation and coloring.

Original issue reported on code.google.com by alexandr...@gmail.com on 24 Jan 2011 at 4:22

zf8848 / protobuf

Syntax coloring doesn't work with emacs 23.1.1 #252