dirmngr: Add a getaddrinfo wrapper backend using ADNS.
* dirmngr/dns-stuff.c: Replace all use of default_errsource. (my_adns_init): Move to top. (resolve_name_adns): New. (resolve_dns_name) [USE_ADNS]: Divert to new func.
- Signed-off-by: Werner Koch <wk@gnupg.org>