[Yhc] Mac issues

Hi, I've been trying to debug the mac ppc, which fails with: src/runtime/BCKernel/thread.c:126: failed assertion `rval==0' The reason is that sem_init returns -1, to indicate error, and an error number that indicates ENOSYS: The function sem_init() is not supported by this implementation. See http://www.opengroup.org/onlinepubs/007908799/xsh/sem_init.html for more details. Of course, I have no idea why sem_init isn't supported, or why its required for a non-threading example, or anything else - just this might help someone else debug this error. Thanks Neil