* certpath.c (find_up): Try to retrieve an issuer key from an
external source and from the ephemeral key DB.
(find_up_store_certs_cb): New.
* keydb.c (keydb_set_ephemeral): Does now return the old
state. Call the backend only when required.
* call-dirmngr.c (start_dirmngr): Use GNUPG_DEFAULT_DIRMNGR.
(lookup_status_cb): Issue status only when CTRL is not NULL.
(gpgsm_dirmngr_lookup): Document that CTRL is optional.
* call-agent.c (start_agent): Use GNUPG_DEFAULT_AGENT.