* lisp/gnus/mm-encode.el (mm-default-file-type): New name

* lisp/gnus/mm-encode.el (mm-default-file-type): New name

Rename from misleading `mm-default-file-encoding`.
(mm-default-file-encoding): Redefine as obsolete alias.

* lisp/mail/sendmail.el (mail-add-attachment):
* lisp/mh-e/mh-mime.el (mh-minibuffer-read-type):
* lisp/gnus/gnus-art.el (gnus-mime-view-part-as-type-internal):
* lisp/gnus/gnus-dired.el (gnus-dired-attach):
* lisp/gnus/mml.el (mml-generate-mime-1, mml-minibuffer-read-type)
(mml-attach-file): Use the new name.