Urlize bug fixes

Created by: dverdin

Two bug fixes for Urlize mode:

1- message text was treated as attachment and remained on the server as either "msg.0.bin" or "msg.0.txt" files. Fixed by testing the part type before urlizing it. 2- some special characters in message id led to the attachment to be considered missing by Sympa.

I also added a test file for Message.t. I only test the _urlize_parts function for now but it is still a start!

Cheers,

David