add hash pseudo property for troubleshooting persistence
major changes, fixed critical bug

There was a serious problem with the rebind template in the allocators, the mmap_allocator relies on the
payload type to name the file, the actual value_type is always char (it is a raw buffer), unfortunately that
RAW_ALLOCATOR was not rebound, that ended up using the same file name for all the pool's persistent buffers
causing segfault.
The code should be simplified: separate heap allocation from mmap allocation, add some sanity check, it should
be possible to detect when more than 1 pool use the same buffer