Adding tests for persistent implementation.
Short circuiting some set functions if called with alias.
Removing illegal reference to different value factory.
Supporting staged mutability on empty sets. After freezing, only immutable operations are supported.

Switching to a new implementation of temp. set writer (effectively the reference implementation) that now leverages staged mutability. This should speed up bulk operations on the writer like addAll().
Removing generics related warnings.
Exporting persistence package.
Changing PDBPersistentHashSet/TrieSet operations to operate with "equivalence" by default.

This is a shortcut that used for the moment to make it compatible with isEqual comparison.