bug#39689: 26.3; browse-url-mail not supporting RFC6068 (UTF-8-Based Percent-Encoding)

[Robert Pluim]

>>>>> On Thu, 20 Feb 2020 14:48:54 +0100, Vegard Vesterheim via "Bug reports 
>>>>> for GNU Emacs, the Swiss army knife of text editors" 
>>>>> <bug-gnu-emacs@gnu.org> said:

    Vegard> Emacs does not seem to correctly handle UTF-8-Based 
Percent-Encoding as
    Vegard> illustrated in Chapter 6.2 from RFC6068.

    Vegard> The command 
    Vegard>    emacs -Q -l browse-url -eval '(browse-url-mail 
"mailto:user@example.org?subject=caf%C3%A9&body=caf%C3%A9";)'

    Vegard> should result in a message buffer with the string "café" insterted 
into the
    Vegard> body part of the message. Instead the string "café" is inserted.

Yes, the assumption in rfc2368-unhexify-string is that percent
escaping is being done of ASCII characters.

epg--decode-percent-escape-as-utf-8 in epg.el does the
right thing, it could be renamed and moved. I think rfc2047 decoding
needs doing on the result as well. Lars, should I just stick these in
rfc2368.el but named something like rfc6068-unhexify-string and
rfc6068-decode-2047-string or something?

Robert