* camel-mime-body-part.[ch]: Remove. We weren't using the fields
that made this different from camel-mime-part, so it basically
just forced us to do lots of gratuitous typecasting.
* camel-multipart.[ch]: Use CamelMimePart. Remove the multipart
parent stuff, since we weren't using that either.
* etc: update for CamelMimeBodyPart -> CamelMimePart
svn path=/trunk/; revision=2645