gpg: Make preferred keyservers work.
* g10/call-dirmngr.c (dirmngr_local_s): Add field set_keyservers_done. (create_context): Move keyserver setting to ... (open_context): here. (clear_context_flags): New. (gpg_dirmngr_ks_get): Add arg override_keyserver. * g10/keyserver.c (keyserver_refresh): Improve diagnostics. (keyserver_get_chunk): Ditto. Pass OVERRIDE_KEYSERVER to ks_get.
It used to ignore the given server but showed a diagnostics that it
will be used.