new page-spacing area

[Graham Percival]

As an addendum to my question about ragged-last-bottom, I wonder
if it would be possible to define new "page areas".  This idea is
inspired by the \newSpacingSection for horizontal spacing -- it
would be nice if we could say

  \newPageArea
(or whatever) and have the page-breaking algorithm (and related
page stuff) reset.  Even laying aside my problems, this could
reduce the time complexity of spacing scores -- dealing with k
problems of size n is easier than dealing with 1 problem of size
n*k.  (assuming the spacing algorithm isn't less than O(n) :)

Cheers,
- Graham