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.
* lisp/gnus/gnus-art.el (article-decode-charset):
* lisp/gnus/gnus-sum.el (gnus-summary-enter-digest-group):
* lisp/gnus/mm-decode.el (mm-dissect-buffer):
* lisp/gnus/nndoc.el (nndoc-decode-content-transfer-encoding)
(nndoc-rfc822-forward-generate-article):
* lisp/mh-e/mh-mime.el (mh-decode-message-body):
Replace mail-header-strip with mail-header-strip-cte.