Bump up version to v1.7.4 for release,
Remove excessive comments from include/class-email-log-list-table.php,
Handle cases where `post_format` or `time_format` are empty

git-svn-id: https://plugins.svn.wordpress.org/email-log/trunk@954193 b8457f37-d9ea-0310-8a92-e5e31aec5664