space profiling

[Henry Cejtin]

It sounds like you like all of my idea except for the run-time cost.  I haven't
actually produced a test of it yet (I will later today), but my claim was that
I can't believe that it would EVER be more than a factor of 4 times slower.
Note that if the program isn't allocating much than the overhead is irrelevant,
and if it is, then the temporary area and allocation bins are all going to
be in L1 cache, which will make this very fast.  I think that it will really
not hurt much at all.
I'll do some tests today hacking up some assembler code to see how much of a
burden it is.