Don't use virtual destructor in addrmap

Don't use virtual destructor in addrmap

The addrmap polymorphism is sort of "phony" in that there isn't really
code in the tree that can be presented with either type.  I haven't
tried to fix this (though perhaps I may); but meanwhile it's handy for
the next patch if addrmap_fixed has a trivial destructor.  This patch
achieves this by making the addrmap destructor non-virtual, and also
making it protected so that objects of any of these types cannot be
destroyed when only the base class is known.