SafeString::purify() and SafeString::of_safe_html(). Removing SafeString::mark_html_safe() since it's no longer needed.
Refactoring of Xss_Security_Test. t() and t2() return a SafeString instance. TODO: - Update all code to use SafeString where appropriate. - Update golden fole of Xss_Security_Test - Stop reporting CLEAN vars in Xss_Security_Test