alias.c:check_alias_name() is not UTF-8 friendly

[Alain Bench <veronatif@…>]

My dear ALL,

    In an UTF-8 environment, entering an alphanumeric alias name at the
<create-alias> prompt suffers from an unexpected interference:

| Alias as: RenéClerc
| Warning: This alias name may not work.  Fix it? ([yes]/no): yes
| Alias as: Ren__Clerc

    The "fix" does replace the 2 bytes constituting René's e acute by an
underscore. Note that if I refuse the fix (replying no), such accented
alias name seemingly works everywhere: Expansion, completion, Aliases
menu, $reverse_alias, save, source... saved within single quotes though:

| alias 'RenéClerc' René Clerc <rene@example.com>

    In a Latin-1 environment, there is no fix proposal, such accented
alias also works everywhere, and saving it does not add single quotes.


Bye!    Alain.
>How-To-Repeat:
>Fix:

[pdmef]

(In [132474d6dd3b]) Make mutt_check_alias_name() multibyte-aware (closes #2403).