This will allow client code to provide more meaningful diagnostics. In
particular it will enable "notmuch new" to continue suggsting the user
run "notmuch setup" to create a config after "notmuch new" is
transitioned to the new configuration framework.
Another fix to the docstrings, this time for the English part of the
docstrings, not the Python class name. No functional changes here.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
