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.
frankly, I'm not found of spaces after parenthesis and before Value variable, I like code to be aligned, but this seems too much for my taste :)