Fine-grained: Make sure all nodes in symbol tables have fullnames if needed

[JukkaL]

If a Node object stored in a symbol table doesn't have a full name defined (i.e. it's None) we can't refresh that node reliably since we have to check that the symbol table node doesn't hold a alias to something else, and we do this comparison using the full name.

If the node can't be refreshed (e.g. variables), a missing full name might still be a problem for AST diff, for example.

[ilevkivskyi]

I have encountered this problem few times when working on strict optional, so I am a big +1 on this. But how is it going to be implemented? If we add asserts before serialization, them this will lead to crashes in short term.

[msullivan]

Have we seen problems with this recently?