[FIX] trackers: Cannot use $this in a closure in PHP 5.3 (not applicable to 13.x as PHP 5.5 is required)

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/12.x@52494 b456876b-0849-0410-b77d-98878d47e9d5