Changed the way we do the TSD area.

Changed the way we do the TSD area.
Now this code is in sysdep.c
Added an element to the TSD to store a pointer to this threads control
structure. This allows a speed up in CtdlThreadSleep(),
CtdlThreadCheckStop() and the odd one or two other places since this
thread no longer needs to search the list of threads to find its own
control ctructure.