* keyedit.c (keyedit_menu): Prompt for subkey removal for both secret and
public subkeys.
* keylist.c (list_keyblock_print), keyedit.c (show_key_with_all_names):
Show the revocation date of a key/subkey, and general formatting work.
* packet.h, getkey.c (merge_selfsigs_main, merge_selfsigs_subkey,
merge_selfsigs): Keep track of the revocation date of a key.
* keydb.h, keyid.c (revokestr_from_pk): New function to print the
revocation date of a key.