Adding `InstantiatorTestAsset\XMLReaderAsset` as of doctrine/instantiator#8 - asset is uncloneable
`InstantiatorTestAsset\XMLReaderAsset` should be instantiable
Backporting doctrine/instantiator#8 hotfix - uncloneable assets should not be attempted to be cloned.
Merge pull request #16 from Ocramius/hotfix/backport-doctrine/instantiator#7-fix

Hotfix/backport doctrine/instantiator#7 fix