dirmngr: Use system certs if --hkp-cacert is not used.
* dirmngr/certcache.c (any_cert_of_class): New var. (put_cert): Set it. (cert_cache_deinit): Clear it. (cert_cache_any_in_class): New func. * dirmngr/http-ntbtls.c (gnupg_http_tls_verify_cb): Add hack to override empty list of HKP certs.
This patch carries the changes for GNUTLS from commit
7c1613d41566f7d8db116790087de323621205fe over to NTBTLS. NTBTLS works
quite different and thus we need to do it this way.
- Signed-off-by: Werner Koch <wk@gnupg.org>