[Aux] Drop unnecessary external entity.

 * Join iterator no longer provider constructor accepting invalidation tag. Instead of this it provides static factory method.
 * All tests have been fixed.
[Aux] Auxiliary metafunction to detect parameter packs with unique types.
[Aux] Static assertion added.
[Code Style] Wording.
[GCC 4.4] Fuck you. Workaround variadic pack expansion.

It evades GCC 4.4 message: "sorry, unimplemented: cannot expand ‘Args ...’ into a fixed-length argument list"