Got rid of a 'FIXME' by implementing a target hook for cleaning up 
private thread info.  Look kosher?

cheers,

Kris

2005-09-29  Kris Warkentin  <kewarken@qnx.com>

    * target.h (struct target_ops): Add new to_delete_extra_thread_info
    hook and define target_delete_extra_thread_info macro.
    * target.c (update_current_target):  INHERIT and de_fault above target
    function.
    * thread.c (free_thread): Call target_delete_extra_thread_info before
    freeing private thread data.