[bp/r52389][FIX] youtube: The YouTube HTML5 player (used by Chrome for instance) needs the allowfullscreen param on the iframe as well these days it seems.

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/12.x@52390 b456876b-0849-0410-b77d-98878d47e9d5