Introduce FileHashMap with signature like:

  FileHashMap(File, Convertor, Policy)

where:
  File points to client provided file used as storage
  Convertor has two methods byte[] toBytes(Object) and Object fromBytes(byte[])
  Policy is one of Policy,MRU(int), Policy.GC(weakrefs|softrefs|timedrefs)
###@###.### 2004-03-04