Fix dictionary checking errors

Fix two errors in dictionary checking that cause or affect unit test failures in the ROOT6 IB:
1) In checkClassDictionary(), if a type does not have a TClass, don't dereference the null TClass pointer in the exception message (doh!), as this segfaults.  Get the type name for the exception message from the type_info.
2) TClass->GetTypeInfo() returns a type_info pointer, not a typeinfo reference. So the pointer returned must be dereferenced in the argument to the TypeID constructor.
Please merge this rerquest as soon as convenient.