This is a mixed commit that fixes various small issues

 * print parentheses
 * 01 is invalid syntax (it was octal in py2)
 * [x for i in 1, 2] is invalid syntax
 * six moves

Signed-off-by: Adrian Tschira <nota@notafile.com>

... instead of creating our own special SQLiteMemoryDbPool, whose purpose was a
bit of a mystery.

For some reason this makes one of the tests run slightly slower, so bump the
sleep(). Sorry.

It turns out that the only thing we use the __dict__ of LoggingContext for is
`request`, and given we create lots of LoggingContexts and then copy them every
time we do a db transaction or log line, using the __dict__ seems a bit
redundant. Let's try to optimise things by making the request attribute
explicit.

Fix a bug where we could end up firing off multiple requests for server_keys
for the same server at the same time.

I'm still unclear on what the intended behaviour for
`verify_json_objects_for_server` is, but at least I now understand the
behaviour of most of the things it calls...

Another signing test vector using an 'm.room.message' with content, so that the implementation will have to redact it