WIP: ENH: avoid potential HashPtrTable memory leaks (#1286)

- in previous versions the HashPtrTable<T> used a HashTable<T*> for
  its underlying storage and added additional routines for deallocating
  memory when items were deleted or the table was cleared.

  This generally works well, but direct use of any HashTable<T*> removal
  methods without additional wrapping results in memory leaks.

  The safer means is to use a container with its own memory management.
  For example, HashTable<autoPtr<T>>.

  Any memory cleanup now becomes automatic.