* test that hiding secret with expired key fails
* add test of user key without username.
* revert to performing most tests with 'user1'.
* move user4 private/public key fixtures
* factor code fetching emails from keyrings, add comments.
* use factored _warn_or_abort()
* add to, clean up, and clarify comments.
* name keys after emails, not usernames
* use emails to specify users
* rename and add function to get emails from keyrings
* rename directories holding gpg test fixtures
* deny emails that aren't in the keyring, and test.
* require 'killperson' emails to exist in keyring
* change test to reflect killperson must use email
* remove no-longer-needed test function
* factor function _assert_keychain_contains_emais()
* fix/make lint happy
