Fix type comparison on OSX

UnknownArrayHandle compares std::type_index objects to check whether a requested type is the same as that held in the array handle. However, it is possible that different translation units can create different but equivalent std::type_info/std::type_index objects. In this case, the == operator might return false for two equivalent types. This can happen on OSX.

To get around this problem, UnknownArrayHandle now does a more extensive check for std::type_info object. It first uses the == operator to compare them (as before), which usually works but can possibly return false when the correct result is true. To check for this case, it then compares the name for the two types and returns true iff the two names are the same.