#6386 #6496 - adding test for uncovered `ValidatorChain#merge()` method, which presents internal type mismatches
#6386 #6496 - fixing values passed internally to `ValidatorChain#attach()` by `ValidatorChain#merge()`
#6386 #6496 - `ValidatorChain` must be cloneable
#6386 #6496 - `ValidatorChain` can be cloned, as the validator chain is now deep-cloned
Merge pull request #6912 from Ocramius/hotfix/#6386-#6496-validator-chain-merge-type-mismatch

Hotfix: #6386 #6496 validator chain merge type mismatch