* tools/card-tool-keys.c (keyblock_cache): New var.
(release_keyblock): Factor code out to a new do_release_keyblock.  Add
a cache.
(flush_keyblock_cache): New.
(get_matching_keys): Use the cache.
* tools/gpg-card-tool.c (cmds): Add command "reset".
(interactive_loop): Implement reset.