gpg: New option --use-only-openpgp-card

* g10/gpg.c (opts): Add option.
(main): Set flag.
* g10/options.h: Add flags.use_only_openpgp_card.
* g10/call-agent.c (start_agent): Implement option.
--

With the previous patch we switch to autoselect an application
instead of requesting an openpgp card.  This option allows to revert
this in case of use use cases which expected the former behaviour.

Signed-off-by: Werner Koch <wk@gnupg.org>
(cherry picked from commit c185f6dfbd)
This was first added to the 2.2 branch.

g10/gpg.c

@@ -426,6 +426,7 @@ enum cmd_and_opt_values
     oKeyOrigin,
     oRequestOrigin,
     oNoSymkeyCache,
+    oUseOnlyOpenPGPCard,
 
     oNoop
   };
@@ -896,6 +897,10 @@ static ARGPARSE_OPTS opts[] = {
   ARGPARSE_s_n (oNoAutostart, "no-autostart", "@"),
   ARGPARSE_s_n (oNoSymkeyCache, "no-symkey-cache", "@"),
 
+  /* Options which can be used in special circumstances. They are not
+   * published and we hope they are never required.  */
+  ARGPARSE_s_n (oUseOnlyOpenPGPCard, "use-only-openpgp-card", "@"),
+
   /* Dummy options with warnings.  */
   ARGPARSE_s_n (oUseAgent,      "use-agent", "@"),
   ARGPARSE_s_n (oNoUseAgent, "no-use-agent", "@"),
@@ -3642,6 +3647,10 @@ main (int argc, char **argv)
             opt.def_new_key_algo = pargs.r.ret_str;
             break;
 
+          case oUseOnlyOpenPGPCard:
+            opt.flags.use_only_openpgp_card = 1;
+            break;
+
 	  case oNoop: break;
 
 	  default: