note 17940 added to function.header

RFC 2616 section 13.13: (...) History mechanisms and caches are different. In particular history mechanisms SHOULD NOT try to show a semantically transparent view of the current state of a resource. Rather, a history mechanism is meant to show exactly what the user saw at the time when the resource was retrieved. (...) All browsers but Opera ignore this. This means Opera _always_ uses cached pages when using back, forward buttons. No matter what headers you send. www.opera.com/support/supsearch/supsearch.cgi?options=index&name=594 -- http://www.php.net/manual/en/function.header.php http://master.php.net/manage/user-notes.php?action=edit+17940 http://master.php.net/manage/user-notes.php?action=delete+17940 http://master.php.net/manage/user-notes.php?action=reject+17940