gpg: Extend --key-origin to take an optional URL arg.

gpg: Extend --key-origin to take an optional URL arg.

* g10/getkey.c (parse_key_origin): Parse appended URL.
* g10/options.h (struct opt): Add field 'key_origin_url'.
* g10/gpg.c (main) <aImport>: Pass that option to import_keys.
* g10/import.c (apply_meta_data): Extend for file and url.
* g10/keyserver.c (keyserver_fetch): Pass the url to
import_keys_es_stream.
--

Example:

  gpg --key-origin url,myscheme://bla --import FILE

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