keyword option can be passed to the pack method.  A false value
  prevents garbage collection.

- The FileStorage constructor now provides a boolean pack_gc option,
  which defaults to True, to control whether garbage collection is
  performed when packing by default. This can be overridden with the
  gc option to the pack method.

The ZConfig configuration for FileStorage now includes a pack-gc
  option, corresponding to the pack_gc constructor argument.

- The FileStorage constructor now has a packer keyword argument that
  allows an alternative packer to be supplied.

The ZConfig configuration for FileStorage now includes a packer
  option, corresponding to the packer constructor argument.