While idn2_to_unicode_8zlz() takes a 'flags' argument, it is ignored and
thus cannot be used to perform IDN checks on the output string.
The bug in libidn2 versions before 2.0.5 was not that a call to
idn2_to_unicode_8zlz() with certain flags set did not cause IDN checks
to be performed. The bug was that idn2_to_unicode_8zlz() did not check
whether a conversion can be performed between UTF-8 and the current
locale's character encoding. In other words, with libidn2 version
2.0.5+, if the current locale's character encoding is ASCII, then
idn2_to_unicode_8zlz() will fail when it is passed any Punycode string
which decodes to a non-ASCII string, even if it is a valid IDNA2008
name.
Rework idn_ace_to_locale() so that invalid IDNA2008 names are properly
and consistently detected for all libidn2 versions and locales.
Update the "idna" system test accordingly. Add checks for processing a
server response containing Punycode which decodes to an invalid IDNA2008
name. Fix invalid subtest description.
Certain characters, like symbols, are allowed by IDNA2003, but not by
IDNA2008. Make dig reject such symbols when IDN input processing is
enabled to ensure BIND only supports IDNA2008. Update the "idna" system
test so that it uses one of such symbols rather than one which is
disallowed by both IDNA2003 and IDNA2008.
