I'm assuming my proposal to extend extent_alloc() et.al. with an additional
argument to allow alignment against arbitrary numbers has met with
implicit approval.

So, I'm going ahead with it in a few days time.


The current `extent_alloc_subregion()' function will become a CPP macro
defined in terms of a new function, probably `extent_alloc_subregion1()',
which takes the extra `skew' parameter.  There'll also be a `extent_alloc1()'
that is the obvious extension of `extent_alloc()'.

-pk