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

in previous versions the HashPtrTable 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>.

Any memory cleanup now becomes automatic.