gpg: Add experimental AKL method "wkd" and option --with-wkd-hash.

* g10/getkey.c (parse_auto_key_locate): Add method "wkd".
(get_pubkey_byname): Implement that method.  Also rename a variable.
* g10/call-dirmngr.c (gpg_dirmngr_wkd_get): New.
* g10/keyserver.c (keyserver_import_wkd): New.
* g10/test-stubs.c (keyserver_import_wkd): Add stub.
* g10/gpgv.c (keyserver_import_wkd): Ditto.
* g10/options.h (opt):  Add field 'with_wkd_hash'.
(AKL_WKD): New.

* g10/gpg.c (oWithWKDHash): New.
(opts): Add option --with-wkd-hash.
(main): Set that option.
* g10/keylist.c (list_keyblock_print): Implement that option.
--

The Web Key Directory is an experimental feature to retrieve a key via
https.  It is similar to OpenPGP DANE but also uses an encryption to
reveal less information about a key lookup.

For example the URI to lookup the key for Joe.Doe@Example.ORG is:

    https://example.org/.well-known/openpgpkey/
    hu/example.org/iy9q119eutrkn8s1mk4r39qejnbu3n5q

(line has been wrapped for rendering purposes).  The hash is a
z-Base-32 encoded SHA-1 hash of the mail address' local-part.  The
address wk@gnupg.org can be used for testing.

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

g10/import.c

@@ -1279,7 +1279,7 @@ import_one (ctrl_t ctrl,
         {
           xfree (*fpr);
           /* Note that we need to compare against 0 here because
-             COUNT gets only incremented after returning form this
+             COUNT gets only incremented after returning from this
              function.  */
           if (!stats->count)
             *fpr = fingerprint_from_pk (pk, NULL, fpr_len);