Remove garbage from Content-Transfer-Encoding value (bug#25420)
* lisp/mail/ietf-drums.el (ietf-drums-strip-cte): New function.
(ietf-drums-remove-garbage): New function.
(ietf-drums-remove-whitespace): Remove CR as well.
* lisp/mail/mail-parse.el (mail-header-strip-cte):
Alias to ietf-drums-strip-cte.