[Mutt] #3518: IDNA2008 support by libidn2 usage in mutt

[Moritz Barsnick]

On Tue, Feb 27, 2018 at 01:56:28 -0000, Mutt wrote:
>  As it is hard (and makes less to no sense) to support IDNA2003 and
>  IDNA2008 in parallel, I would recommend to replace IDNA2003 by IDNA2008
>  support, which means that the requirement in the end switches over from
>  libidn to libidn2 simply.

This is probably still very welcome, e.g. for mutt-1.10 (wow, are we
there already, it seems like only yesterday we were stuck at 1.4.xx
forever ;->).

The patch, which you integrated into the Fedora package, as I noticed,
it not completely correct syntactically, as it continues to use the
legacy return code checks (IDNA_SUCCESS) while libidn2 provides its own
(e.g. IDN2_OK). Pre-2017 versions of libidn2 didn't provide the legacy
enums.

Moritz