* thread.cc (pthread::create): Use PTHREAD_DEFAULT_STACKSIZE stacksize

	* thread.cc (pthread::create): Use PTHREAD_DEFAULT_STACKSIZE stacksize
	if attr.stacksize is 0.
	(pthread_attr::pthread_attr): Initialize stacksize to 0 to align more
	closely to Linux.
	(pthread_attr_getstack): Fix incorrect stackaddr computation.  Return
	stackaddr just like pthread_attr_getstackaddr.  Remove slightly off
	comment.
	(pthread_attr_getstackaddr): Remove slightly off comment.
	(pthread_getattr_np): Return stackaddr and stacksize based on the full
	allocated stackarea.