Free Tennis 0.4.8.

Free Tennis 0.4.8, by Maurizio Colucci.
I wondered about this, but I don't think it's actually bash-specific: it's [in the Open Group spec](http://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_03) and supported by at least ash/dash.