Re: BUG #18763: pg_get_viewdef returns an old def with new relation name

It seems like an old, raw viewdef has already been obtained from pg_rewrite before it was blocked by first connection. 

Then in `get_query_def`, it tries to parse the raw viewdef. 

Before finishing its work, `get_query_def` will acquire locks and wait until first connection finishes. 

After that, during the parsing process, relation names are finally generated by `generate_relation_name` in ruleutils.c using `SearchSysCache1`.

And `SearchSysCache1` will use the catalog snapshot to get the latest relname. 

Perhaps we should refer to the code of `pg_get_constraintdef_worker`, directly using `systable_beginscan` with transaction snapshot?

Regards

Lin Yuzhe