Add a type that stores chunks of data in its own storage and avoids
duplicates. Supported methods:

ha_storage_create()
Allocates new storage object.

ha_storage_put()
Copies a given data chunk into the storage and returns pointer to the
copy. If the data chunk is already present, a pointer to the existing
object is returned and the given data chunk is not copied.

ha_storage_empty()
Clears (empties) the storage from all data chunks that are stored in it.

ha_storage_free()
Destroys a storage object. Opposite to ha_storage_create().

Approved by:	Marko