#73 eve dead space on fill with

[Ralph Thomas]

From Sean Parent...

What's happening is that the length is getting measured by summing
the children (and space and guides and margins...) and max'ed against
the container length. The additional_length cross stream comes from
subtracting the length in that direction from each child. But that
doesn't work with stream - here the additional_length is coming from
the extra space the container has within it's parent (there is an
assumption that the calculated length is minimal).