* gnus-art.el (gnus-decode-address-function): New variable.

* gnus-art.el (gnus-decode-address-function): New variable.
(article-decode-encoded-words): Use it to decode headers which are
 assumed to contain addresses.
(gnus-mime-delete-part): Remove useless `or'.

* gnus-sum.el (gnus-decode-encoded-address-function): New variable.
(gnus-summary-from-or-to-or-newsgroups): Use it to decode To header.
(gnus-nov-parse-line): Use it to decode From header.
(gnus-get-newsgroup-headers): Ditto.
(gnus-summary-enter-digest-group): Use it to decode `to-address'.

* mail-parse.el (mail-decode-encoded-address-region): New alias.
(mail-decode-encoded-address-string): New alias.

* rfc2047.el (rfc2047-quote-special-characters-in-quoted-strings):
 New function.
(rfc2047-encode-message-header, rfc2047-encode-region): Use it.
(rfc2047-strip-backslashes-in-quoted-strings): New fnction.
(rfc2047-decode-region): Use it; add optional argument `address-mime'.
(rfc2047-decode-string): Ditto.
(rfc2047-decode-address-region): New function.
(rfc2047-decode-address-string): New function.