[PATCH] threading fix, tid-2.5.47-A3

[PATCH] threading fix, tid-2.5.47-A3

This introduces the sys_set_thread_address() syscall.  It sets the tid
address (which gets cleared at VM release time) and returns the PID so
that the newly initialized 'initial thread' does not have to do an
additional sys_gettid() call.

It is used to bootstrap a thread group where the original thread user
hasn't had a tid address assigned to it by any parent.