More lenient IDNA processing in dig

By default, DiG now uses a "lax" IDN mode (when compiled with libidn2 and when the output is a terminal), This enables transitional IDN processing, so that DiG can consume and display IDNA2003 names that exist in the DNS. If there are any problems with IDN processing, DiG will quietly handle the name as if IDN were disabled. This means that international query names are rendered verbatim on the wire, and ACE names are printed raw without conversion to UTF8.

Users who want IDNA2008 conformance can use the new +idn=strict option to turn it on. For backwards compatibility the old +idnin and +idnout options can still be used to enable or disable strict IDNA2008 separately for input and output. These old spellings are now aliases for +idn=in and +idn=out.

Originally inspired by #3485 (closed) and later moved to more relaxed issue #3527 (closed)