Fix validation for array with set of types (refs #31)

This is a fix for #31 

Setting current_schema to the actual type being checked against fixes the 'no_extra_properties_allowed' issue mentioned. 

I'm still not happy about the actual error reporting because whatever you do, it would only report a "wrong_type". No matter if there are actual bad additional properties, missing properties or additional items.
the same here, don't particularly like extra spaces, if you want to align the result (false), just alight arrows (->)