Use require_once in more places

I got:
PHP Fatal error:  Cannot redeclare file_notice() (previously declared in /etc/inc/notices.inc:55) in /etc/inc/notices.inc on line 91
So there are places that notices.inc gets require() when already required.
Use require_once in more places
Use require_once in more places
Use function_exists test
Use function_exists test
Merge pull request #1149 from phil-davis/patch-7