o Add stub support for some new futex operations,

	o	Add stub support for some new futex operations,
		so the annoying message is not printed.

	o	Don't warn about FUTEX_FD not being implemented
		and return ENOSYS instead of 0 (eg. success).

	o	Clear FUTEX_PRIVATE_FLAG as we actually implement
		only private futexes so there is no reason to
		return ENOSYS when app asks for a private futex.
		We don't reject shared futexes because they worked
		just fine with our implementation so far.

Approved by:	kib (mentor)
Tested by:	bsam
MFC after:	1 week