Add kbnode_t for easier backporting.

* g10/global.h (kbnode_t): New.
gpg: Fix regression due to the keyserver import filter.

* g10/keyserver.c (keyserver_retrieval_filter): Change args.  Rewrite
to take subpakets in account.
* g10/import.c (import_one, import_secret_one): Pass keyblock to
filter.
--

GnuPG-bug-id: 1680

Resolved conflicts:
	g10/main.h - s/import_filter/import_filter_t/g