[v3] __pool_alloc rework

[Paolo Carlini]

Hi Carlo,

>Hiya,
>
>since you guys are constantly rewriting the pool allocator
>anyway ;)
>
;)

> ... I was wondering if I can ask for an extension
>that will more or less stay stable.
>
my radical proposal (only for discussion): the original SGI allocator 
had both a
MT mode and a non-MT mode (without locks). What about providing now only
the /latter/, since for MT applications we really want to suggest 
mt_alloc and the
performance of pool_alloc are rather poor anyway??

Paolo.