#72 Overridden members cause problems with xml_pack

[High Performance Coder]

An inheritance like the following

struct A
{
     map<int,string> foo;
 };

 struct B: public A
 {
        map<int,string> foo;
}     

does not work properly with xml_pack/xml_unpack. xml_unpack will attempt to unpack B::foo from "B#0.foo#0.pair, whereas the actual data is stored under B#0.foo#1.pair.