mpool_filter
mpool_filter(t->bt_mp, __bt_pgin, __bt_pgout, t);
mpool_filter(hashp->mp, __pgin_routine, __pgout_routine, hashp);
void mpool_filter __P((MPOOL *, void (*)(void *, db_pgno_t, void *),
void mpool_filter(MPOOL *, void (*)(void *, pgno_t, void *),
mpool_filter(t->bt_mp, __bt_pgin, __bt_pgout, t);