When checking cryptographic signatures, Notmuch relies on GMime to
tell it whether the certificate that signs a message has a valid User
ID or not.
If the User ID is not valid, then notmuch does not report the signer's
User ID to the user. This means that the consumer of notmuch's
cryptographic
Several functions in test/test-lib.sh used variable names that are
also used outside of those functions (e.g. $output and $expected are
used in many of the test scripts), but they are not expected to
communicate via those variables.
We mark those variables "local" within test-lib.sh so that they
