tablesorter: add latest version 2.15.4

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@50021 b456876b-0849-0410-b77d-98878d47e9d5
[FIX] PluginBox: $style parameter was missing its $ and a couple of other nits

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@50022 b456876b-0849-0410-b77d-98878d47e9d5