Remove all the "double return" statements which were a result of us removing all the instances of
```
defer.returnValue(...)
return
```
statements when we switched to python3 fully.
Python will return a tuple whether there are parentheses around the returned values or not.
I'm just sick of my editor complaining about this all over the place :)
Currently when fetching state groups from the data store we make two
hits two the database: once for members and once for non-members (unless
request is filtered to one or the other). This adds needless load to the
datbase, so this PR refactors the lookup to make only a single database
hit.
There is no reason to return a tuple of tokens when the last token is
always the token passed as an argument. Changing it makes it consistent
with other storage APIs
While I was going through uses of preserve_fn for other PRs, I converted places
which only use the wrapped function once to use run_in_background, to avoid
creating the function object.
