Testing monotonic clock

[Matthew Dillon]

:I hate when it happens ;).
:
:OK, I ended up bringing in some changes from FreeBSD - I verified these 
:and these make perfect sense. I haven't verified yet what it breaks in 
:our tree :).
:
:The source of the problem seems to be the stuff we have in sys/_posix.h. 
:Besides being buggy, using these defines doesn't make sense IMHO. 
:Volunteers to review (and kill?) it?

    Looks ok to me.  As much as I don't like repeating definitions,
    this is probably the cleanest way to do it for now.

   					-Matt