[css3-transforms] Missing text about transforms inducing an abs-pos containing block

The spec says "The object acts as a containing block for fixed positioned
descendants." It also needs to say that the object is a containing block
for abs-pos descendants too.

Rob
-- 
“You have heard that it was said, ‘Love your neighbor and hate your enemy.’
But I tell you, love your enemies and pray for those who persecute you,
that you may be children of your Father in heaven. ... If you love those
who love you, what reward will you get? Are not even the tax collectors
doing that? And if you greet only your own people, what are you doing more
than others?" [Matthew 5:43-47]