agent: Add command DELETE_KEY.

* agent/command.c (cmd_delete_key): New.
* agent/findkey.c (modify_description): Add '%C' feature.
(remove_key_file): New.
(agent_delete_key): New.
* agent/command-ssh.c (search_control_file): Make arg R_DISABLE
optional.

* configure.ac: Require libgpg-error 1.13.
gpg: Change pinentry prompt to talk about "secret key".

* g10/passphrase.c (gpg_format_keydesc): Add mode 2.  Change strings.
* g10/keydb.h (FORMAT_KEYDESC_NORMAL, FORMAT_KEYDESC_IMPORT)
(FORMAT_KEYDESC_EXPORT): New.  Use them for clarity.
--

The use of the term "certificate" was more confusing than helpful.
gpg: Fix regression in secret key export.

* agent/cvt-openpgp.c (convert_to_openpgp): Fix use
gcry_sexp_extract_param.
* g10/export.c (do_export_stream): Provide a proper prompt to the
agent.
--

NB: The export needs more work, in particular the ECC algorithms.
gpg: Re-indent a file.

* g10/delkey.c: Re-indent.
(do_delete_key, delete_keys): Change return type top gpg_error_t.
gpg: Re-enable secret key deletion.

* g10/call-agent.c (agent_delete_key): New.
* g10/keydb.h (FORMAT_KEYDESC_DELKEY): New.
* g10/passphrase.c (gpg_format_keydesc): Support new format.
* g10/delkey.c (do_delete_key): Add secret key deletion.
Two minor code cleanups and one NULL deref on error fix.

* common/estream.c (es_freopen): Remove useless check for STREAM.
* kbx/keybox-blob.c (_keybox_create_x509_blob): Remove useless check
for BLOB.
* tools/sockprox.c (run_proxy): Do not fclose(NULL).
--

Found by Hans-Christoph Steiner with cppcheck.
common: Add z-base-32 encoder.

* common/zb32.c: New.
* common/t-zb32.c: New.
* common/Makefile.am (common_sources): Add zb82.c
(module_tests): Add t-zb32.
gpg: New %U expando for the photo viewer.

* g10/photoid.c (show_photos): Set namehash.
* g10/misc.c (pct_expando): Add "%U" expando.
--

This makes is possible to extract all photos ids from a key to
different files.