fails:Array#flatten performs respond_to? and method_missing-aware checks when coercing elements to array
fails:Array#flatten with a non-Array object in the Array does not call #to_ary if not defined when #respond_to_missing? returns false
fails:Array#flatten with a non-Array object in the Array calls #to_ary if not defined when #respond_to_missing? returns true
fails:Array#flatten with a non-Array object in the Array calls #method_missing if defined
