<txp:yield />: Avoid name collisions between tag handler and reserved PHP keyword.
 
 Required for PHP 5.5 compatibility.
 Fixes issue #383.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5501 2fea6a4d-a838-0410-917b-93a53c48e9d2