examples/ostest: Works around a bug in printf() when cancellation points are...

examples/ostest:  Works around a bug in printf() when cancellation points are enabled.  printf() is a cancellation point because it calls write().  This is correct according to OpenGroup.org.  However, printf holds the stdio library semaphore when it is canceled and this leaves the semaphore in a bad state.  No fix for the printf bug yet.