Print out more useful info in ast_map::node_id_to_str

[catamorphism]

Right now, node_id_to_str doesn't print out very useful info for ctor, dtor, local, arg, or export nodes. It should.

[catamorphism]

Not very important (though not difficult either); milestoning as far-future.

[msullivan]

Actually, it might be tricky to get more useful information for some of these, without having more data structures to use than just the ast_map. node_arg in particular.