Rewrite old tag dispatching switch to use XTL generalization

[solodon4]

We have a set of macros implement matching in those cases where we rely on tags instead of RTTI. We can let the user express relation between his tagged classes using XTL primitive and see if it would fit in the same way boost::variant did. The only problem I can immediately see is the substitutability loop that was iterating over base tags, but maybe we don't need it.