sm: Consider certificates w/o CRL DP as valid.

* sm/certchain.c (is_cert_still_valid): Shortcut if tehre is no DP.
* common/audit.c (proc_type_verify): Print "n/a" if a cert has no
distribution point.
* sm/gpgsm.h (opt): Add field enable_issuer_based_crl_check.
* sm/gpgsm.c (oEnableIssuerBasedCRLCheck): New.
(opts): Add option --enable-issuer-based-crl-check.
(main): Set option.
--

If the issuer does not provide a DP and the user wants such an issuer,
we expect that a certificate does not need revocation checks.  The new
option --enable-issuer-based-crl-check can be used to revert to the
old behaviour which requires that a suitable LDAP server has been
configured to lookup a CRL by issuer.

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

sm/gpgsm.c

@@ -146,6 +146,7 @@ enum cmd_and_opt_values {
   oDisableTrustedCertCRLCheck,
   oEnableTrustedCertCRLCheck,
   oForceCRLRefresh,
+  oEnableIssuerBasedCRLCheck,
 
   oDisableOCSP,
   oEnableOCSP,
@@ -412,6 +413,8 @@ static gpgrt_opt_t opts[] = {
   ARGPARSE_s_n (oDryRun, "dry-run", N_("do not make any changes")),
   ARGPARSE_s_s (oRequestOrigin,   "request-origin", "@"),
   ARGPARSE_s_n (oForceCRLRefresh, "force-crl-refresh", "@"),
+  ARGPARSE_s_n (oEnableIssuerBasedCRLCheck, "enable-issuer-based-crl-check",
+                "@"),
   ARGPARSE_s_s (oAuditLog, "audit-log",
                 N_("|FILE|write an audit log to FILE")),
   ARGPARSE_s_s (oHtmlAuditLog, "html-audit-log", "@"),
@@ -1268,6 +1271,9 @@ main ( int argc, char **argv)
         case oForceCRLRefresh:
           opt.force_crl_refresh = 1;
           break;
+        case oEnableIssuerBasedCRLCheck:
+          opt.enable_issuer_based_crl_check = 1;
+          break;
 
         case oDisableOCSP:
           ctrl.use_ocsp = opt.enable_ocsp = 0;