gpg: Improve WKD by importing only the requested UID.
* g10/keyserver.c: Include mbox-util.h. (keyserver_import_wkd): Do not use the global import options but employ an import filter.
We also make sure that an mbox has been passed to keyserver_import_wkd
so it may also be called with a complete user id (which is currently
not the case).
- Signed-off-by: Werner Koch <wk@gnupg.org>