nptl/TODO

   1 - we should probably extend pthread_mutexattr_t with a field to create a
   2   single linked list of all instances.  This requires changing the
   3   pthread_mutexattr_* functions.
   4
   5
   6 - a new attribute for mutexes: number of times we spin before calling
   7 sys_futex
   8
   9
  10
  11 - test with threaded process terminating and semadj (?) being applied
  12   only after all threads are gone