agent: Add option --no-allow-external-cache.
* agent/agent.h (opt): Add field allow_external_cache. * agent/call-pinentry.c (start_pinentry): Act upon new var. * agent/gpg-agent.c (oNoAllowExternalCache): New. (opts): Add option --no-allow-external-cache. (parse_rereadable_options): Set this option.
Pinentry 0.9.2 may be build with libsecret support and thus an extra
checkbox is displayed to allow the user to get passwords out of an
libsecret maintained cache. Security aware user may want to avoid
this feature and may do this at runtime by enabling this option.
- Signed-off-by: Werner Koch <wk@gnupg.org>