* camel-mime-message.[ch]: Remove the "session" field from
CamelMimeMessage. Nothing uses it, about half of the existing
calls to camel_mime_message_new_with_session pass NULL, and
there's no obvious reason for it to be there.
* others: Use camel_mime_message_new instead of
camel_mime_message_new_with_session
svn path=/trunk/; revision=2479