Things that aren't done yet
                   ---------------------------

1. Implement PTHREAD_PROCESS_SHARED for semaphores, mutexes,
   condition variables, read/write locks, barriers.

2. For version 3 onwards: the following types need to change, resulting in an ABI
   change:

   a) ptw32_handle_t (a.k.a. pthread_t)
   Change the reuse counter from unsigned int to size_t. Type "int" on 32 bit
   and 64 bit Windows is 32 bits wide.
   
   To give an indication of relative effectiveness of the current "unsigned int",
   consider an application that creates and detaches threads at the rate of 1
   per millisecond. At this rate the reuse counter will max out after 49 days.

   After changing to "size_t" an application compiled for x64 and creating and
   detaching a thread every nanosecond would max out after 584 years.

   b) pthread_once_t
   Remove unused elements.