gpgsm: Allow sepcification of ldaps servers.

* sm/gpgsm.h (struct keyserver_spec): Add field use_ldaps.
* sm/gpgsm.c (parse_keyserver_line): Parse flags.
* sm/call-dirmngr.c (prepare_dirmngr): Send ldaps flag to the dirmngr.
* dirmngr/dirmngr.h (struct ldap_server_s): Add field use_ldaps.
* dirmngr/ldapserver.c (ldapserver_parse_one): Parse flags.
* dirmngr/ldap.c (start_cert_fetch_ldap): Call wrapper with --tls.
* dirmngr/dirmngr_ldap.c: New option --tls.
(fetch_ldap): Make use of that option.

There was no way to specify an LDAPS server in
dirmngr_ldapserver.socnf or with gpgsm's --keyserver option. This
patch fixes this. Eventually we should allow to replace host and port
by a partial URI in the same way ldap_initialize does it. For backward
compatibility we do not yet do that.

Although the dirmngr code accepts an URL (eg. taken from a
certificate), I can't see how the scheme was ever used. Thus the
patch also detects an ldaps scheme and uses this. That part has not
been tested, though.

• Signed-off-by: Werner Koch <wk@gnupg.org>