integral conversion policy for bstreams #63

Please provide an integral conversion policy about what to do when
  - converting from size_t to uint32_t
and
  - size of both types differ.

Please refer to the comment in 
http://code.google.com/p/mili/source/detail?r=338&url_prefix=p for further 
details.

If types are equal (32bits), then the policy should just be ignored. This could 
be achieved with a policy type mapper:
   ConversionPolicy<size>::Policy
(where Policy can be many).