This test stubbed out some stuff in a very weird way. I have no idea why. It broke.

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.

Fixes a bug introduced in https://github.com/matrix-org/synapse/pull/1783 which
meant that single backslashes were not allowed in event field filters.

The intention here is to allow single-backslashes, but disallow
double-backslashes.

Broadly three things here:

* disable W504 which seems a bit whacko
* remove a bunch of `as e` expressions from exception handlers that don't use
  them
* use `r""` for strings which include backslashes

Also, we don't use pep8 any more, so we can get rid of the duplicate config
there.

Thanks @Half-Shot !!!

This test didn't do what it claimed to do, and what it claimed to do was the
same as test_cant_hide_direct_ancestors anyway.

This stuff is tested by sytest anyway.

Signed-off-by: Schnuffle <schnuffle@github.com>

when processing incoming transactions, it can be hard to see what's going on,
because we process a bunch of stuff in parallel, and because we may end up
recursively working our way through a chain of three or four events.

This commit creates a way to use logcontexts to add the relevant event ids to
the log lines.

I spent ages trying to figure out how I was going mad...

Older Twisted (18.4.0) returns TimeoutError instead of
ConnectingCancelledError when connection times out.
This change allows tests to be compatible with this behaviour.

Signed-off-by: Oleg Girko <ol@infoserver.lv>

ExpiringCache required that `start()` be called before it would actually
start expiring entries. A number of places didn't do that.

This PR removes `start` from ExpiringCache, and automatically starts
backround reaping process on creation instead.

We want to wait until we have read the response body before we log the request
as complete, otherwise a confusing thing happens where the request appears to
have completed, but we later fail it.

To do this, we factor the salient details of a request out to a separate
object, which can then keep track of the txn_id, so that it can be logged.

Use the actual origin for push transactions, rather than whatever the remote
server claimed.