Split check_flags() off check_keys() and have check_exprs() call it later, so its error messages gain an "in definition" line. Tweak the error messages. Checking values in a function named check_keys() is unclean anyway. Signed-off-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Message-Id: <20190927134639.4284-20-armbru@redhat.com>