Make purge history slightly faster

Fix handling of redacted events from federation

* fix

* changelog

If we receive an event that doesn't pass their content hash check (e.g.
due to already being redacted) then we hit a bug which causes an
exception to be raised, which then promplty stops the event (and
request) from being processed.

This effects all sorts of federation APIs, including joining rooms with
a redacted state event.

Don't pull out events that are outliers and won't be deleted, as nothing
should happen to them.

expose number of real reserved users

Log outbound requests when we retry

Change the manhole SSH key to have more bits

fix VOIP crashes under Python 3

add some logging for the keyring queue

Fix jwt import check

Timeout reading body for outbound HTTP requests

* speed up room summaries by pulling their data from room_memberships rather than room state
* disable LL for incr syncs, and log incr sync stats  (#3840)

Newer versions of openssh client refuse to connect to the old key due to
its length.

Remove build requirements after building docker image